Removing the CMOS battery
There are times when it becomes necessary to clear the CMOS settings in your computer. You may have changed something in the CMOS that will not allow your computer to boot. This is especially true when an attempt has been made to overclock the computer to make it run faster. Most motherboards have a jumper that you can change to reset the CMOS, but it is small and can be a pain to work with. The easiest way to reset your CMOS settings is to remove the CMOS backup battery.
Instructions
1. Turn off the computer. Remove the power cord. Unplug any network or modem cables. Turn off your monitor, any printers, scanners, speakers or any other devices.
2. Remove the left side cover.
3. Find the CMOS battery on the motherboard. It is a silver disc about the size of a quarter. It is held in a plastic holder by a small metal clip. Before you remove the battery, touch an unpainted part of the case to eliminate any static buildup. Push down on the clip with a small flat-head screwdriver. While holding down the clip, flip out the battery with your fingertip.
Tags: CMOS battery, CMOS settings, down clip, your computer