Sometimes the computer’s BIOS (Basic Input Output System) can become corrupt. This can cause Windows to fail to boot or malfunction when the operating system cannot properly communicate with your hardware. On these occasions, you can reset the BIOS to its default configuration.
The first and easiest way to reset the computer’s BIOS is to access the BIOS by pressing Delete or F2 on your keyboard at startup and then restore the default BIOS settings.
Your motherboard, which houses your BIOS chip, has a CMOS battery and a BIOS/CMOS reset button or jumper. You can remove the battery for between 20 seconds and two minutes to reset the CMOS.
1. Place the PC on a level, firm surface, and make sure it is turned off and disconnected from the electrical outlet. Ground yourself by touching an unpainted area on the PC case, using an anti-static wristband if possible, and open the side of the PC to expose the motherboard.
2. Locate the battery on the motherboard. It looks like (and, indeed, is) a large watch battery. Unclip the battery to remove it from the motherboard.
3. There is a Clear CMOS jumper on the motherboard, close to the battery; check the motherboard manual for the exact location. The jumper is three pins with a small connector covering two of them. Remove the connector, and move it to cover the center pin and the uncovered pin. A small pair of tweezers is useful for doing this.
4. Leave the jumper as described in step 3 for 10 seconds, and then move it back to its original position.
5. Replace the motherboard battery.
6. Reassemble the PC case, and reconnect it to the main power supply.
On some motherboards, instead of a CMOS jumper, there is a small reset button on the back of the panel.
This button, which you can normally press with a paper clip, can make it easier to reset the BIOS.
If you find that you can’t use new hardware with your PC, you might need to update your computer’s BIOS to a newer version. To do this, check your motherboard manual or the support section of the manufacturer’s website.
Source of Information : Microsoft Press - Troubleshooting Windows 7 Inside Out