Should You Reset the CMOS? When It Helps and When It Doesn’t

4 Aug 2026

Resetting the CMOS is one of those computer fixes that appears in almost every troubleshooting guide.

A desktop will not start, the BIOS settings look wrong, new memory is unstable, or the computer keeps returning to the firmware screen. Someone then suggests clearing the CMOS as though it were a universal repair.

Sometimes it is exactly the right step.

A CMOS reset can restore safe firmware defaults, remove an unstable overclock, correct a bad boot configuration, or recover a motherboard after incompatible hardware settings were saved.

But it will not repair Windows, recover a failed SSD, replace a dead motherboard battery, or fix damaged hardware. It can also trigger BitLocker recovery and remove settings that were essential to the computer’s previous configuration.

The key is knowing what a CMOS reset actually changes—and what it leaves untouched.

What Is CMOS?

Historically, CMOS referred to a small amount of low-power memory used to store BIOS configuration settings.

Modern computers may store firmware settings differently, but the phrase clear the CMOS is still widely used to mean:

Reset the BIOS or UEFI configuration to its default values.

These settings can include:

Boot order
Date and time
Secure Boot configuration
Storage-controller mode
Memory profiles
CPU settings
Fan behaviour
Virtualisation
Integrated-device settings
Network boot
Trusted Platform Module settings
Power-management options
Fast Boot
Hardware monitoring thresholds

A CMOS reset does not usually erase the operating system or personal files. It changes the motherboard’s firmware configuration.

What a CMOS Reset Does

Depending on the computer, clearing the CMOS may:

Load the motherboard’s default firmware settings
Remove overclocking values
Disable custom memory profiles
Restore automatic CPU voltages
Reset the boot order
Return storage settings to their defaults
Restore default fan curves
Reset the system clock
Re-enable or disable integrated hardware
Clear certain failed hardware-training values
Remove a firmware setting that prevents startup

It is essentially a way of telling the motherboard:

Forget the customised configuration and try the standard settings again.

What a CMOS Reset Does Not Do

Clearing the CMOS does not normally:

Delete Windows
Remove personal files
Format the SSD
Repair corrupted system files
Fix a physically failed drive
Remove malware
Repair a broken motherboard
Replace faulty RAM
Recover a damaged BIOS installation
Fix a failing power supply
Repair a cracked display
Remove an account password from Windows
Restore deleted data
Update the BIOS

It is a firmware-configuration reset, not a general computer reset.

When Resetting the CMOS Can Help

There are several situations where clearing the CMOS is a sensible troubleshooting step.

The Computer Will Not Start After a BIOS Change

A firmware setting can prevent the system from completing startup.

Examples include:

Incorrect memory timings
Unsupported CPU settings
Manual voltage changes
An unstable overclock
Incorrect graphics configuration
Disabled storage controller
Wrong PCIe mode
Aggressive Fast Boot settings

If the computer stopped starting immediately after a BIOS change, a CMOS reset can restore safer defaults.

This is one of the strongest reasons to use it.

An Overclock or Undervolt Is Unstable

Manual CPU, GPU, or memory tuning can cause:

Black screens
Restart loops
Freezing at the manufacturer logo
Failure to enter the BIOS
Random crashes
Memory errors
Failure to complete POST

A CMOS reset removes most motherboard-level tuning and allows the hardware to run at standard values.

Any separate graphics-card settings applied through Windows software may need to be reset independently.

An XMP or EXPO Memory Profile Prevents Booting

XMP and EXPO profiles allow memory to run at advertised performance settings rather than basic default speeds.

Most compatible systems handle this correctly, but instability can occur because of:

Unsupported memory kit
Mixed memory modules
Weak memory controller
Incorrect BIOS version
Excessively high memory speed
Four-module configurations
Manual timing changes

If enabling XMP or EXPO causes a black screen or startup loop, clearing the CMOS can return the memory to conservative default settings.

Some motherboards will recover automatically after several failed starts, but not all do.

The Computer Is Stuck in a POST Loop

POST is the motherboard’s initial hardware-checking process.

A system that repeatedly starts, stops, and restarts before Windows loads may be struggling with:

Memory training
Firmware settings
CPU configuration
Recently installed hardware
Incorrect voltage
PCIe configuration

A CMOS reset can help when the loop is caused by stored firmware values.

It will not help if the underlying hardware is faulty.

The BIOS Settings Have Become Corrupted

Firmware settings can occasionally become inconsistent after:

Failed overclocking
Power interruption
Firmware update
Hardware replacement
Battery failure
Repeated failed starts
Incorrect configuration changes

Loading defaults through the BIOS menu is preferable when the computer still works.

A physical CMOS reset is more useful when you cannot reach the firmware interface.

The Computer Will Not Recognise Newly Installed Hardware

A reset can sometimes help the firmware rediscover hardware after installing:

New RAM
Graphics card
CPU
NVMe SSD
PCIe card
Network adapter
Storage controller

However, first confirm that the component is:

Compatible
Properly seated
Correctly powered
Installed in the right slot
Supported by the current BIOS version

A CMOS reset cannot make unsupported hardware compatible.

The Boot Order Is Completely Wrong

A BIOS reset can remove an incorrect boot sequence that causes the system to:

Start from an old drive
Attempt network boot
Loop into a USB installer
Skip Windows Boot Manager
Return directly to the BIOS

However, resetting the CMOS may also change a previously correct boot order.

After the reset, confirm that Windows Boot Manager on the correct internal drive is selected first.

The System Is Using the Wrong Graphics Output

Firmware settings can sometimes force a display through:

Integrated graphics
Dedicated graphics card
A particular PCIe slot
An external graphics device

If the screen remains blank after a hardware change, resetting the CMOS may restore automatic graphics selection.

Before doing that, test:

Another display cable
Another monitor
The motherboard video output
The graphics-card output
One monitor at a time

The BIOS Password Has Been Forgotten

On some older or custom-built desktop systems, clearing the CMOS may remove a firmware setup password.

On many modern laptops and business devices, it will not.

Enterprise computers may store firmware credentials in protected memory that is not cleared by removing the battery.

Do not assume a CMOS reset will bypass security.

For company-owned systems, follow the manufacturer’s and organisation’s authorised recovery process.

The Date and Time Keep Resetting

Clearing the CMOS may temporarily correct the clock, but it does not solve the underlying cause if the date and time keep being lost.

Repeated clock resets often indicate:

Weak CMOS battery
Failed motherboard battery circuit
Firmware issue
Motherboard fault

The usual repair is replacing the small motherboard battery, commonly a CR2032 in desktops, and then restoring the correct BIOS settings.

Laptop battery arrangements vary and may require disassembly.

When a CMOS Reset Probably Will Not Help

A CMOS reset is often suggested for faults it cannot realistically solve.

Windows Is Slow

Clearing the CMOS is unlikely to improve ordinary Windows performance.

A slow computer is more commonly affected by:

Limited RAM
Full storage
Failing drive
Background applications
Malware
Windows updates
Browser overload
Thermal throttling
Old hardware

Resetting firmware may even reduce performance if it disables an approved memory profile.

Windows Will Not Load but the BIOS Works Normally

If the computer passes POST and reaches:

Automatic Repair
Blue screen
Spinning dots
Windows recovery
Sign-in failure

the fault may belong to Windows, drivers, updates, or the storage device rather than CMOS settings.

Use Windows Recovery tools and assess the drive before resetting firmware unnecessarily.

The SSD or Hard Drive Has Failed

A CMOS reset cannot repair a drive that is:

Missing from the BIOS
Reporting SMART errors
Clicking or grinding
Disconnecting repeatedly
Failing diagnostics
Producing read errors

It may help only if the drive is hidden because of an incorrect controller setting.

If important data is stored on a failing drive, avoid repeated startup attempts and intensive repair scans.

The BIOS Update Failed

Clearing the CMOS does not reinstall damaged firmware.

A failed BIOS update may require:

Manufacturer recovery procedure
USB BIOS recovery
Dual-BIOS recovery
BIOS Flashback
Replacement firmware chip
Motherboard repair or replacement

Use only instructions for the exact model.

The Motherboard Is Physically Faulty

A reset cannot repair:

Burnt components
Failed voltage regulators
Damaged socket pins
Liquid damage
Cracked board
Failed chipset
Short circuit
Corroded contacts

It may appear to help temporarily if a faulty component behaves intermittently, but the underlying defect remains.

The RAM Is Faulty

A CMOS reset may allow unstable memory settings to return to default.

It will not repair a defective memory module.

Run built-in diagnostics or a proper memory test if you see:

Random crashes
Memory errors
Beep codes
Startup loops
Corrupted files
Blue screens with different error codes

The Power Supply Is Failing

A weak power supply can produce symptoms that resemble firmware trouble:

Failure to start
Restart loops
Drives disappearing
Graphics card not initialising
Freezes during POST
Random shutdowns

Clearing the CMOS will not restore stable power.

The Computer Has Malware

Malware generally operates inside the operating system, browser, firmware, or connected accounts.

A CMOS reset does not remove:

Viruses
Adware
Ransomware
Browser hijackers
Remote-access tools
Compromised passwords

Use approved security scanning and incident-response procedures.

Before You Reset the CMOS

A CMOS reset is not normally destructive to files, but it can have serious side effects.

Take these precautions first.

Make Sure You Have the BitLocker Recovery Key

Firmware changes can cause BitLocker to request its recovery key.

This can happen after changes to:

Secure Boot
TPM
Boot order
Storage controller
BIOS settings
Firmware measurements

Before resetting the CMOS, confirm that the BitLocker recovery key is available.

It may be stored in:

Microsoft account
Microsoft Entra ID
Active Directory
Device-management platform
Printed or saved recovery record
IT provider’s secure documentation

Do not clear the TPM as part of a routine CMOS reset.

Photograph the Existing BIOS Settings

When the firmware is still accessible, record important settings.

Photograph or note:

Boot order
Storage-controller mode
Secure Boot
UEFI or Legacy mode
TPM status
Virtualisation
Fan settings
XMP or EXPO
Integrated-device configuration
Network boot
Date and time

This makes it easier to restore settings that the defaults change.

Back Up Important Data

A CMOS reset does not normally erase data.

However, changing the storage mode or boot settings incorrectly afterwards can prevent Windows from starting.

Back up important files before major firmware troubleshooting whenever possible.

Disconnect Unnecessary External Devices

Before assuming the CMOS is responsible, remove:

USB drives
External storage
Docking stations
Memory cards
Printers
USB hubs
Non-essential PCIe devices
Unnecessary displays

A connected device may be blocking POST or changing the boot sequence.

Try Loading BIOS Defaults First

If you can enter the BIOS, use its built-in reset option rather than opening the computer.

Look for:

Load Setup Defaults
Load Optimised Defaults
Restore Defaults
Reset to Default
Factory Defaults

Save the changes and restart.

This normally achieves the same configuration reset with less physical risk.

Ways to Reset the CMOS

The exact method depends on the motherboard or computer.

Always consult the manufacturer’s instructions.

Method 1: Use the BIOS Menu

This is the safest method when the firmware remains accessible.

Enter BIOS or UEFI
Find the option to restore defaults
Confirm the reset
Save and exit
Re-enter BIOS afterwards
Restore required settings

This avoids opening the case.

Method 2: Use a Clear-CMOS Button

Some desktop motherboards and high-end systems include a dedicated button.

It may be located:

On the rear input/output panel
On the motherboard
Inside the case

The system normally needs to be powered down first.

Follow the manual carefully, as button behaviour differs between models.

Do not confuse the CMOS button with BIOS Flashback or another firmware control.

Method 3: Use the Motherboard Jumper

Desktop motherboards may include pins labelled:

CLR_CMOS
CLRTC
JBAT1
CLEAR
CMOS

The process may involve moving a jumper or briefly bridging two pins while the computer is disconnected from power.

Using the wrong pins can damage the motherboard.

Only follow the exact motherboard manual.

Method 4: Remove the CMOS Battery

Some desktop motherboards use a coin-cell battery.

A typical process is:

Shut the computer down
Disconnect the power cable
Press the power button briefly to discharge residual power
Observe antistatic precautions
Remove the coin-cell battery
Wait for the period specified by the manufacturer
Reinstall it in the correct orientation
Reconnect power
Enter BIOS and restore settings

Removing the battery for a few seconds may not always clear every setting. Follow the board instructions.

Do not use metal tools carelessly around the motherboard.

Laptop CMOS Resets Are Different

Modern laptops may not have an easily accessible coin-cell battery.

Firmware settings may be retained through:

Internal battery
Separate RTC battery
Embedded controller
Protected non-volatile storage

Reset procedures may involve:

Holding the power button
Manufacturer recovery key sequence
Disconnecting the internal battery
Service-mode switch
Dedicated reset hole
BIOS recovery utility

Opening the laptop may risk:

Warranty issues
Damaged clips
Torn cables
Battery puncture
Static damage
Broken connectors

Use the manufacturer’s service documentation or professional assistance.

What to Expect After the Reset

The first startup may take longer than normal.

The motherboard may:

Retrain the memory
Detect hardware again
Restart more than once
Display a checksum warning
Request confirmation of defaults
Ask you to set the date and time
Return directly to BIOS
Change fan speed temporarily

Do not interrupt a legitimate memory-training process unless it continues far beyond the manufacturer’s expected time.

Settings You May Need to Restore

After clearing CMOS, check the following.

Boot Order

Ensure the correct Windows installation is selected.

For most modern systems, this will be:

Windows Boot Manager

rather than the raw drive name, USB device, or network boot.

UEFI or Legacy Mode

Windows 11 systems normally use UEFI.

Switching the firmware to Legacy or Compatibility mode can make the existing installation appear unbootable.

Restore the mode used when Windows was installed.

Storage-Controller Mode

Check whether the system previously used:

AHCI
RAID
Intel RST
VMD
Manufacturer-specific storage mode

A change can trigger an Inaccessible Boot Device error.

Do not guess. Use the recorded original setting.

Secure Boot

Secure Boot may return to its default state.

Windows 11 systems normally expect it to be available, but changing it can trigger BitLocker recovery or affect custom operating systems.

Restore the approved configuration.

XMP or EXPO

Memory will normally return to a basic standard speed.

Do not immediately re-enable the performance profile if memory instability was the original problem.

Test the system at defaults first.

Fan and Thermal Settings

Custom fan curves may be lost.

Confirm that:

Fans are detected
CPU temperature is normal
Pump headers are configured correctly
Silent mode is not causing overheating
Water-cooling settings are restored where required

Incorrect fan or pump settings can cause rapid overheating.

Virtualisation

Features such as Intel VT-x, AMD-V, IOMMU, or related options may return to default.

This can affect:

Hyper-V
Virtual machines
Windows Sandbox
WSL features
Security products
Credential Guard
Development tools

Restore them only when required.

Integrated Devices

The reset may change whether the following are enabled:

Audio
Wi-Fi
Bluetooth
Onboard network adapter
SATA ports
Integrated graphics
USB controllers
Serial ports
Thunderbolt
Camera or biometric devices

If hardware disappears after the reset, check these settings.

Date and Time

Set the correct date, time, and time zone.

A wrong clock can cause:

Certificate errors
Failed website access
Sign-in problems
Update failures
Incorrect logs
Domain-authentication problems

If the time keeps resetting, replace or assess the CMOS battery.

Signs the CMOS Reset Helped

The reset was probably useful when:

The computer now completes POST
BIOS becomes accessible again
The display returns
Memory is detected correctly
Startup loops stop
The system boots at default settings
A newly installed component appears
Overclocking-related crashes stop
The correct boot device can be selected
Firmware settings no longer behave unpredictably

Do not immediately reapply every previous custom setting.

Add changes one at a time and test.

Signs the Problem Lies Elsewhere

Investigate hardware or software when:

The drive remains undetected
The motherboard shows the same error code
The computer still has no power
RAM diagnostics fail
The system continues restarting at defaults
The BIOS is visibly corrupted
The computer overheats
The SSD produces errors
Windows fails after firmware checks complete
There are burning smells, liquid damage, or damaged components

Repeatedly clearing CMOS is not a repair strategy.

Could Resetting CMOS Make Things Worse?

It can create additional work or temporarily stop Windows from starting if important settings are lost.

Possible consequences include:

Wrong boot order
Storage-mode change
BitLocker recovery prompt
Secure Boot change
Lost fan configuration
Disabled virtualisation
Network boot being enabled
Memory running at a lower speed
Wrong date and time
Integrated hardware becoming disabled
Business security configuration being altered

This is why business computers should not be reset without recording the existing configuration and recovery information.

CMOS Reset vs BIOS Update

These are different procedures.

CMOS Reset

Clears firmware settings and restores defaults.

BIOS Update

Replaces or updates the firmware code itself.

A reset can resolve a bad configuration.

An update may resolve:

Hardware compatibility
Firmware bugs
Security vulnerabilities
Stability problems
Storage detection
CPU support

Do not update the BIOS simply because a CMOS reset did not work.

First identify whether the update addresses the actual fault.

CMOS Reset vs Power Reset

A power reset removes residual electrical state.

It may involve:

Shutting down
Disconnecting power
Holding the power button
Reconnecting power

This does not necessarily erase the BIOS settings.

Try a power reset before a CMOS reset when the computer has become unresponsive after:

Sleep
Docking issue
Power cut
Peripheral fault
Static discharge
Battery depletion

CMOS Reset vs Windows Reset

They are unrelated.

CMOS Reset

Restores motherboard firmware settings.

Reset This PC

Reinstalls Windows while offering options to keep or remove personal files.

Do not use Reset This PC to solve a firmware configuration problem, and do not expect a CMOS reset to repair Windows files.

A Practical Decision Guide

Consider clearing the CMOS when:

The problem began immediately after changing BIOS settings
An overclock, undervolt, XMP, or EXPO profile caused instability
The system will not complete POST
You cannot reach BIOS after a configuration change
New compatible hardware is not being initialised
Boot configuration is clearly wrong
The manufacturer recommends it for the exact symptom

Do not make it the first choice when:

Windows alone is slow
A drive is clicking or failing diagnostics
The computer has no power
Malware is suspected
The display panel is damaged
The operating system is corrupted
The motherboard has obvious physical damage
The BIOS update itself failed

A Safe Troubleshooting Order

Use this sequence before physically clearing CMOS:

Photograph any error codes
Disconnect non-essential devices
Perform a full power reset
Try entering BIOS
Load firmware defaults through the menu
Check drive detection and boot order
Confirm the BitLocker recovery key is available
Record important BIOS settings
Follow the exact manufacturer CMOS-reset procedure
Allow memory training to complete
Re-enter BIOS and restore required settings
Test the computer at default values
Run hardware diagnostics
Investigate RAM, storage, power, or motherboard faults if the problem remains

When to Contact an IT Professional

Professional assistance is recommended when:

The device uses BitLocker and the recovery key is unavailable
The computer is company-managed
The storage-controller mode is unknown
A laptop must be dismantled
The motherboard has no clear CMOS instructions
The drive is missing or failing
The system reports memory or CPU errors
The BIOS update failed
Custom cooling or overclocking settings are involved
Important data is not backed up
The system remains unable to complete POST
Clearing the CMOS temporarily fixes the fault but it keeps returning

A technician can record the existing firmware configuration, reset it safely, test the motherboard and connected hardware, and restore the correct boot, encryption, storage, and security settings.

Reset the CMOS for the Right Reason

Clearing CMOS is useful when the motherboard is trapped by a bad firmware configuration.

It can recover systems affected by unstable memory profiles, overclocking, incorrect boot settings, hardware-detection problems, and certain POST failures.

It will not repair damaged Windows files, recover a failed SSD, remove malware, or fix physically faulty hardware.

Before resetting it, secure the BitLocker recovery key, record the existing BIOS settings, and try loading defaults through the firmware menu. After the reset, confirm the boot order, storage mode, Secure Boot, fan settings, and system clock before starting Windows.

Hamilton Group can diagnose BIOS and startup faults, reset firmware safely, resolve boot-order and BitLocker issues, test memory and storage, and recover business computers that will not start.

Call 0330 043 0069 or visit hgmssp.com to book a meeting with one of our IT experts.