Take off the PC case and look for a small battery (similar to a watch battery) located on the motherboard. You will see a jumper with 3 pins next to the battery, and a peice of plastic covering pin numbers 1-2. Take off the plastic and place on pin numbers 2-3 for roughly 10 seconds. Put the plastic back to it's original position. You have now cleared the CMOS and the password.
When you reboot you will need to enter the CMOS to reapply your settings, as they would have been cleared also