All motherboards require some form of electrical power supply to operate. However, even when a motherboard is not receiving power from an external source, some electricity is still maintained on the motherboard due to capacitors and the motherboard's CMOS battery. The CMOS battery keeps all of the settings in the computer's BIOS, such as the device configuration and local time setting. You can drain the power from the motherboard by removing the CMOS battery temporarily.
Power off the computer, if it is powered on, and disconnect the power cord.
Remove the side cover of the computer case. Some cases have screws while others use a movable lever.
Disconnect the 20- or 24-pin ATX main power connect from the motherboard.
Disconnect the 4- or 8-pin 12V ATX connector from the motherboard
Remove the CMOS battery from the motherboard for a few minutes. This will drain all of the power residing in the motherboard.
If you reinsert the CMOS battery and reassemble the computer, the BIOS settings are reset to their factory defaults and may need to be reconfigured.
In some cases, the steps in this article can be used to remove a BIOS password.