Key takeaways
- How to reset CMOS on a motherboard: BIOS defaults, clear button, jumper and battery methods ordered safest first, plus what resets and what can go wrong.
To reset CMOS, restore the BIOS settings to their factory defaults, either from inside the setup screen or, if the computer will not start, by clearing the memory that holds them with a button, a jumper or by removing the small coin battery with the power disconnected. The reset affects firmware settings only, not your files. Reasons to do it include a failed overclock, a forgotten BIOS password, a no-display problem after a hardware change, or odd behaviour after a firmware update. This guide orders the methods from the safest to the most involved.
What CMOS is and what a reset changes
CMOS refers to a small memory area on the motherboard that stores the BIOS or UEFI settings. A coin battery, usually a CR2032, keeps it alive when the computer is unplugged, which is how the clock stays right. Clearing it returns settings to the maker’s defaults.
Expect these to change: the date and time, boot order, memory tuning profiles such as XMP or EXPO, fan curves, voltage and overclock settings, and any setup password. Drive data is untouched. A few settings, for instance a drive controller mode, may need to be set again for the operating system to start. Because your custom choices disappear, photograph the BIOS screens before you start whenever the computer still works.
Before you begin: preparation and warnings
- Shut the computer down, switch the power supply off and unplug the power cable from the wall. Reset steps must happen with all power removed unless the manual says otherwise.
- Touch bare metal on the case to discharge static, and handle the board by its edges.
- Keep the manual open at the page that shows the jumper or button.
- If your drive is encrypted, find your recovery key first, because changed firmware settings can prompt for it.
- Remember that opening the case is normally fine for warranty purposes, but damage from forced parts is not covered.
With that done, work through the methods in order and stop as soon as one works.
Method 1: load defaults from inside the BIOS
If you can still reach the setup screen, this is the safest option. Restart and press the key shown at startup, commonly Delete or F2, then look for an option such as Load Optimized Defaults, Load Setup Defaults or Reset to Default. Confirm, then save and exit. Nothing is opened, nothing is unplugged, and the board does the work.
It will not help when the computer shows no picture or will not reach setup, but it is the right first move for a bad tuning profile or a boot order that went wrong. Take a moment to reapply important settings afterwards, such as the memory profile and the boot drive.
Method 2: the clear CMOS button
Some boards have a button on the rear panel or on the board itself, labelled Clear CMOS, CMOS Clr or similar. On boards that have one, this is the easiest hardware method. With the computer off and the power cable removed, press and hold the button for a few seconds, as the manual instructs. Some models need the power supply switched on at the wall for the button to work, while others require it off; the manual gives the exact rule for that board, so follow it rather than guessing.
Release the button, reconnect the power cable and start the computer. A message such as “CMOS settings wrong” or “BIOS has been reset” is normal on the first start.
Method 3: the jumper
Most boards have a three-pin jumper, or a two-pin header, near the battery or the bottom edge, often labelled CLR_CMOS, CLRTC or JBAT. In the normal position a small plastic cap covers pins 1 and 2. Follow these steps:
- Power down, switch off the supply and unplug the cable from the wall.
- Press the case power button for several seconds to drain leftover charge.
- Move the cap to pins 2 and 3, or bridge the two pins if the header has only two, and hold it there for the time stated in the manual, commonly around ten seconds.
- Return the cap to its original position. Leaving it in the clear position can stop the board from starting or from keeping settings.
- Reconnect the power and boot.
Hold the cap with fingers or plastic tweezers. Avoid using a metal screwdriver to bridge pins unless the manual specifically allows it, since a slip can short nearby parts.
Method 4: removing the battery
Use this when no button or jumper exists, or those methods failed. With everything unplugged and the discharge step done, find the coin battery. A small metal clip holds it; push the clip gently aside with a fingernail or a plastic tool and the cell pops up. Leave it out for a few minutes, press the power button once more to drain the circuit, then insert a battery with the positive side facing up, as it was, until it clicks.
If the clip is stiff, stop and reassess rather than prying. A graphics card may block access, in which case remove it first, carefully, with the power off. A weak battery that fails to hold the clock is worth replacing with the same type while it is out.
What to expect after the reset
The first start is often slower, and the board may restart once while it retrains memory. You may see a prompt to enter setup or press a key to continue. Set the date and time, confirm the boot drive is listed, then re-enable the memory profile if you used one. If your board expects a firmware refresh to support a newer processor, see how to update your motherboard BIOS for the careful way to do it, including keeping power stable and never interrupting an update.
What can go wrong and when to stop
If there is still no display after a reset, check that memory modules and the graphics card are fully seated, and that the monitor cable is plugged into the graphics card rather than the board. If the drive is encrypted and asks for a recovery key, enter it, then consider it a reminder to keep that key safe. If the system powers on but stays blank after several attempts, repeated resets will not help.
Stop and seek support in these cases: a bent socket pin, a torn battery holder, a burning smell, or no response after the steps above. Check the warranty terms, and contact the manufacturer with the exact board model before attempting further repairs.
A worked example: recovering from a failed overclock
Suppose a computer shows no picture after a memory speed increase. Power it down, unplug it, find CLR_CMOS in the manual and clear the memory with the jumper, then return the cap. Reconnect, boot, and set the date. Next, load defaults, save, and restart. Once it is stable, apply the memory profile only, without further changes, and test in normal use before pushing any further. Write down each setting you change, so the next problem is easy to trace.
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Frequently asked questions
Does resetting CMOS delete any files?
No. Clearing CMOS resets firmware settings stored on the board, such as boot order, clock and tuning options, not the data on your drives. Your operating system and files stay where they are. The reset may change how the board sees your drives, such as a storage mode, so the system might not start until you restore the setting in the BIOS.
How long should the battery stay out?
Manuals and guides vary, from about thirty seconds to a few minutes, and some boards want the power supply unplugged for the whole time. Follow the manual for your board if it gives a figure. Holding the power button with the cable removed first drains leftover charge, which helps the memory chip fully clear.
Does a CMOS reset remove the BIOS password?
Often, yes, because the setup password is typically stored in the same settings memory. Some systems, notably laptops and certain prebuilt machines, store it elsewhere and a normal reset will not clear it. If a reset does not remove it on a desktop board, check the manual or contact the manufacturer for the supported route.
Is it safe to reset CMOS after a failed overclock?
It is the standard recovery step when settings stop the computer from starting. Unplug the power cable first, use the clear button, jumper or battery method described in your manual, and then start with defaults. Reapply tuning in small steps afterwards, so you can see which change caused the problem.
Why does the computer take longer to start after a reset?
After defaults are restored, the board often retrains the memory and rechecks hardware, which can take longer than a normal start, and it may restart once or twice. Give it a few minutes with the screen on. If it still shows nothing, stop and follow the troubleshooting steps in the manual rather than repeating resets.
