|Did anything happen to it between the last time it worked OK and the first time it didn't?|
Sometimes Intel motherboards allow for a 'bios recovery' using a dos boot disk with the bios file that runs on its own. Check your motherboard manual as you may need to configure a bios recovery jumper. Some info here too:
But I think you're just assuming the problem is with the bios. If the problem is elsewhere a recovery attempt won't help.