Just spotted this @ Sudhian.com.

Whilst scouring the web for the latest hardware news, I've stumbled across what appears to be a widespread problem with many nForce2 motherboards, that is resulting in unbootable machines. There appears to be a significant problem with the BIOS on a variety of nForce2 motherboards that leads them to become spontaneously corrupted following a reboot, leaving the machine unbootable. The only solution found so far, seems to be to replace the BIOS chip, or somehow re-flash the original using another machine.