How to Clear CMOS (Reset the BIOS): 3 Safe Methods, Step by Step

In this guide (6 sections)

• What clearing the CMOS does, and what it doesn’t
• When should you clear the CMOS?
• The three methods
• After you clear the CMOS
• When clearing the CMOS doesn’t help
• Real cases: what other users ran into

Clearing the CMOSClear CMOS: Resetting the motherboard's settings back to factory defaults. It doesn't delete your files. More in our Startup & BIOS glossary →Close ✕ means resetting your motherboardMotherboard: The large main circuit board inside the PC that every other part plugs into. More in our PC basics glossary →Close ✕’s BIOSBIOS (UEFI): The motherboard's built-in settings program, which starts the PC before Windows. You open it with Delete or F2 at startup. More in our Startup & BIOS glossary →Close ✕ settings to factory defaults. It’s the standard fix when a setting, like a RAMRAM (memory): Memory modules: short-term working space the PC needs to run. They clip into slots next to the processor. More in our PC basics glossary →Close ✕ overclock or a changed boot option, stops the PC from starting or showing a picture. It’s safe, it doesn’t touch your files, and it takes a few minutes.

What clearing the CMOS does, and what it doesn’t

It does	It doesn’t
Reset every BIOS setting to factory defaults	Delete your files, programs or Windows
Undo a failed RAM overclock (XMPXMP / EXPO: A one-click BIOS setting that runs RAM at its advertised faster speed. If unstable, the PC may not start. More in our RAM & storage glossary →Close ✕/EXPO) or CPU overclock	Undo a BIOS updateBIOS update: A new version of the motherboard's built-in software, often needed to support newer processors. More in our Startup & BIOS glossary →Close ✕: your BIOS version stays the same
Reset the boot orderBoot order: The list in the BIOS that decides which drive the PC tries to start Windows from first. More in our Startup & BIOS glossary →Close ✕ and the date and time	Fix a faulty part, such as a dead module of RAM or a broken graphics cardGPU (graphics card): The graphics card: the part that creates the picture you see on the monitor. More in our PC basics glossary →Close ✕
Fix a black screen caused by a video or startup setting	Fix a wiring mistake or a short circuitShort circuit: Electricity taking a path it shouldn't, for example through the case. The PC then shuts off to protect itself. More in our Startup & BIOS glossary →Close ✕

The name comes from the small memory chip, the CMOS, where older PCs stored these settings, kept alive by the CMOS battery. Modern motherboards store them differently, but the name stuck.

When should you clear the CMOS?

It’s worth trying when:

• The PC stopped starting, or the screen went black, right after you changed a BIOS setting (XMP, EXPO, overclocking, boot options, video settings).
• The PC doesn’t get past POSTPOST: Power-On Self-Test: the quick check the PC runs every time you switch it on, before Windows loads. More in our Startup & BIOS glossary →Close ✕ and you’ve already checked the cables. See our no-POST guide for the full checklist.
• A debug lightDebug lights: Four small lights on the motherboard (CPU, DRAM, VGA, BOOT). The one that stays on shows where startup got stuck. More in our Startup & BIOS glossary →Close ✕ stays on after a BIOS change. See what the debug lights mean.
• You’re going to fit a new processorCPU (processor): The processor: the chip that does most of the computer's thinking. It sits under a cooler on the motherboard. More in our PC basics glossary →Close ✕ or RAM and want to start from clean settings.

It’s not worth trying when the PC shows no sign of power at all: that’s a power or button problem (see newly built PC won’t turn on).

The three methods

Three ways to clear the CMOS

Use whichever your motherboard has. The result is the same: BIOS settings back to factory defaults.

First, always: shut down, switch the power supply to O, and unplug the power cable.

1. The button

Rear ports of the PC

Press and hold it for about 5 seconds.

The easiest. Found on many mid-range and high-end motherboards.

2. Two metal pins on the motherboard

Pins on the motherboard, often near the battery

Touch both pins together with a metal screwdriver for 5–10 seconds.

Check the manual for the exact pins. Touch only those two.

3. The battery

Coin battery on the motherboard

Pop the round battery out, wait 5 minutes, then put it back the same way up.

Works on every motherboard. It may sit under the graphics card.

Whatever the method, start the same way: shut down, switch the power supply off and unplug its power cable. For methods 2 and 3, also touch a metal part of the case first to discharge any static.

Method 1: the Clear CMOS button

Many mid-range and high-end motherboards have a small button on the back panel, among the USB ports, labeled CLR CMOS or BIOS reset.

1. With the PC unplugged, press and hold the button for about 5 seconds.
2. Plug the PC back in and switch it on.

It’s the easiest method because you don’t need to open the case.

Method 2: the jumper pins

Almost every motherboard has two small pins for clearing the CMOS, labeled CLRTC, CLR_CMOS, JBAT1 or similar. They’re often near the coin battery or the bottom edge of the motherboard. Your manual shows exactly where.

1. With the PC unplugged, open the side panel.
2. Find the two pins. Touch both at the same time with the tip of a metal screwdriver for 5–10 seconds. Some motherboards come with a small plastic cap (a jumper) to place over the pins instead.
3. Remove the screwdriver or jumper, close the case, plug in and start the PC.

Touch only those two pins, nothing else.

Method 3: remove the battery

This works on every motherboard, though it can take a little longer.

1. With the PC unplugged, open the side panel and find the round, coin-sized battery (usually a CR2032). It’s sometimes hidden under the graphics card, which you may need to remove first.
2. Press the small metal clip next to it and lift the battery out.
3. Wait at least 5 minutes. Pressing the case power button a few times while it’s out helps drain any remaining power.
4. Put the battery back the same way up (the + side usually faces up), close the case, plug in and start.

After you clear the CMOS

• Be patient with the first start. The motherboard retrains the RAM, which can take 1–3 minutes on DDR5 PCs with a black screen. Don’t switch off halfway.
• You may see a message such as “CMOS settings wrong” or “Press F1”. That’s normal: press F1 or Delete to enter the BIOS.
• Set the date and time, and check the boot drive is the one with Windows.
• Change settings one at a time. If XMP or EXPO caused the problem, try setting the RAM one speed step lower than its rated speed (how to find a stable speed), or leave it at default.

When clearing the CMOS doesn’t help

If the PC still won’t start after a reset, a setting wasn’t the cause. The usual next suspects:

• RAM: test one module at a time in the slot your manual recommends.
• A BIOS too old for your processor: clearing the CMOS won’t fix this; you need a BIOS update, which some motherboards can do without a working CPU. See how to check BIOS support.
• Cables, shorts or a faulty part: see PC turns on then off and the no-POST guide.

And if you find yourself clearing the CMOS again and again, every time you save a setting, that points to a problem with the motherboard or its BIOS. Try a BIOS update, and if that doesn’t help, contact the seller.

Real cases: what other users ran into

These are real reports from PC forums, summarized in our own words, with a link to each original thread.

Real caseASRock B850M-CSolvedBlack screen in the BIOS after changing boot optionsRead what happened

Two days into a newly built PC, the owner changed some boot options. From then on the screen stayed black until Windows loaded, even when entering the BIOS, on every video output. Following a forum suggestion, they cleared the CMOS using a jumper borrowed from an old motherboard, and the BIOS screen came back. A separate issue with a second boot drive remained.

Takeaway: a black screen that started right after a BIOS change is exactly what clearing the CMOS fixes. See the three methods.

Source: ASRock Forum

Real caseASRock B650 Riptide · Ryzen 5 7600 · G.Skill DDR5-5600Solved by replacing hardwareHad to clear CMOS after every BIOS saveRead what happened

Every time the owner saved anything in the BIOS, even with no changes, the PC got stuck in a boot loop. Clearing the CMOS fixed it, but only until the next save. They tried three RAM kits, several BIOS versions and a second identical motherboard, and contacted support. In the end they switched to a different brand of motherboard, which worked as it should.

Takeaway: needing to clear the CMOS repeatedly isn’t normal. It points to the motherboard or its BIOS. See when clearing doesn’t help.

Source: ASRock Forum

Real caseASRock B550M Pro4 · Ryzen 7 3700X · Corsair DDR4-3600Not solved by the userClearing the CMOS didn't bring it backRead what happened

After the owner manually set the RAM to 3600 in the BIOS, the PC stopped starting. They cleared the CMOS in several ways, including leaving the battery out overnight. The PC then reached the logo but restarted in a loop. Advice to try one module of RAM and raise the memory voltage didn’t help either, and the owner requested a replacement.

Takeaway: a reset undoes settings, not hardware problems. If it doesn’t help, move on to testing the RAM and the motherboard. See when clearing doesn’t help.

Source: ASRock Forum

Frequently asked questions

Is clearing the CMOS safe?

Yes. It only resets settings to the factory defaults. Just make sure the PC is unplugged first, and when using the pin method, touch only the two marked pins.

Will clearing the CMOS delete my files or Windows?

No. Your files and Windows are on your drives, which aren’t affected. You may need to check the boot drive in the BIOS afterwards.

How long should I leave the battery out?

At least 5 minutes. Pressing the power button a few times while it’s out helps drain any leftover power.

Does clearing the CMOS undo a BIOS update?

No. It resets settings, but the BIOS version stays the same. Going back to an older version needs a separate BIOS flash.

My PC shows “CMOS checksum error” at every start. What does that mean?

Usually that the CMOS battery is running flat, so the settings are lost whenever the PC is unplugged. Replacing the CR2032 battery normally fixes it.