[Zantham]

While you can reset your CMOS by removing the battery, using the jumper is the correct way to reset your CMOS. I use the terms BIOS and CMOS in this post interchangeably.

EDIT Feb07: Due to new information (thanks Subman1), in most (all?) motherboards you must also remove the battery when using the CMOS clear jumper to properly reset the CMOS. Shorting the battery terminals like I mention below is not necessary in this case, since this is what happens when you move the jumper to the clear position with the battery removed. I have added the appropriate steps below (2.5 and 3.5). I don't know if this applies to motherboards that have a Clear CMOS button usually located on the back I/O panel (placed there for people that like to clear their CMOS often ie: overclockers, so they don't have to open their case all the time).

** Ensure you remove all static from yourself by either using a grounded anti-static strip, or touching the computer's power supply before touching any other electronic component.

1) Locate your clear CMOS jumper (or BIOS reset). Note that just because it is near your battery doesn't necessarily mean that that is the correct jumper. Reference your motherboard manual to find the correct jumper. Some motherboards also have a jumper to reset the password, this does not reset the rest of your CMOS to default values however. Sometimes you can find instructions right on the motherboard itself indicating what pins are used.

2) Shut down your computer so it turns off. Unplug the power. Note that unplugging the power is very important - many computers still use some power to the motherboard even when powered off. Generally there is an LED somewhere on the motherboard that remains lit even if the system is shut off but still plugged into the wall. After you unplug the power from the wall, often I will press the power button once more to drain the capacitors (it is not unusual for the fans to twitch or even spin for a second when I do this, even with the system disconnected from the wall.) Any LEDs on the motherboard should now be unlit.

edit: 2.5) Locate the battery on your motherboard. Most motherboards take a CR2032 battery that is approximately 3/4 of an inch in diameter (2cm). Very carefully remove the battery from the motherboard (you may need a small thin-bladed screwdriver). Note carefully which way the battery was facing before you remove it... you do not want to put it in backwards!

3) Typically the CMOS reset (may also be called BIOS reset by some) is a 3-pin jumper. The jumper cap will usually, but not always, be on pins 1 and 2. You clear the CMOS by removing the jumper, and placing them on pins 2 and 3 (or 1 and 2, depending where it was to start). Leave it there for 10 seconds minimum. Then remove the jumper and replace it back on the original pins.

edit: 3.5) Replace the battery back into its holder, making certain you have not put it in backwards.

4) Plug in and power up your system. You should get an error that your CMOS or BIOS setting have been changed, or some other similar error message, at this point you go into your computers CMOS settings, and have fun resetting all your configurations. Generally the default BIOS settings are not the optimal settings, and occasionally, particularily in higher-end systems, your computer may not even boot; for example some RAM requires a higher voltage to run and will not run at the default voltages. You must either plug in some other RAM to reprogram your RAM to run at the higher voltage, hopefully you have some lying around, sometimes you can just plug in a single stick and it may boot allowing you to set your voltage back to the required settings. I mention the RAM here as an example since it is the most likely event to occur.

5) Note that resetting your CMOS will not correct a badly flashed BIOS, nor will it fix a corrupted BIOS (in certain circumstances it may), nor will it correct the problem if you flashed your system with an incorrect BIOS. Sometimes your BIOS will get corrupted by a power spike or voltage drop within the motherboard, resetting the BIOS will most often fix this type of problem.

To reset your CMOS by taking out the battery:

** Ensure you remove all static from yourself by either using a grounded anti-static strip, or touching the computer's power supply before touching any other electronic component.

1) Shut down your computer so it turns off. Unplug the power. Note that unplugging the power is very important - many computers still use some power to the motherboard even when powered off. Generally there is an LED somewhere on the motherboard that remains lit even if the system is shut off but still plugged into the wall. After you unplug the power from the wall, often I will press the power button once more to drain the capacitors (it is not unusual for the fans to twitch or even spin for a second when I do this, even with the system disconnected from the wall.) Any LEDs on the motherboard should now be unlit.

2) Locate the battery on your motherboard. Most motherboards take a CR2032 battery that is approximately 3/4 of an inch in diameter (2cm). Very carefully remove the battery from the motherboard (you may need a small thin-bladed screwdriver). Note carefully which way the battery was facing before you remove it... you do not want to put it in backwards!

3) I generally short the motherboards battery terminals with a paperclip or a screw driver. This drains the CMOS capacitor and will reset your CMOS faster. Or if you so choose, you can just leave the computer unplugged, with no battery in it, for 30 mins or more, some computers will reset quite fast, others I've had take over 24 hours before the capacitor finally drained (which is why I choose to just short out the terminals on the motherboard).

4) Replace the battery back into its holder, making certain you have not put it in backwards.

5) Plug in and power up your system. You should get an error that your CMOS or BIOS setting have been changed, or some other similar error message, at this point you go into your computers CMOS settings, and have fun resetting all your configurations. Generally the default BIOS settings are not the optimal settings, and occasionally, particularily in higher-end systems, your computer may not even boot; for example some RAM requires a higher voltage to run and will not run at the default voltages. You must either plug in some other RAM to reprogram your RAM to run at the higher voltage, hopefully you have some lying around, sometimes you can just plug in a single stick and it may boot allowing you to set your voltage back to the required settings. I mention the RAM here as an example since it is the most likely event to occur.

6) Note that resetting your CMOS will not correct a badly flashed BIOS, nor will it fix a corrupted BIOS (in certain circumstances it may), nor will it correct the problem if you flashed your system with an incorrect BIOS. Sometimes your BIOS will get corrupted by a power spike or voltage drop within the motherboard, resetting the BIOS will most often fix this type of problem.