Sounds like you may need to reset the BIOS. You would need to find a manual for your motherboard, or find something online with the info.
It's pretty simple, they are just reset by a jumper on the motherboard. The location of the jumper varies by motherboard, which is why you need the manual with the location. Some newer motherboards, however, have a BIOS reset button, which is easily spotted by looking at the motherboard.