I had 2 MOBO-s P4SP-MX with same problem.

I had 2 MOBO-s P4SP-MX with same problem. In both cases it was bad contact on eprom socket. When I removed socket and soldered Eprom directly on board, MOBO`s started normaly. ( To be frank, I also had one of these mobos that had diferent problem that was related with BIOS too I couldn`t solve - It didn`t want to boot from MOBO bios and period!)