Sometimes you can remove the CMOS battery and all the RAM and reboot a couple of times. Then when you put it all back in, if it comes up with "BIOS checksum error defaults loaded" you are in luck.

That trick has worked for me several times. Not last time, that thing did run, I reloaded Win 7 in it and even registered it. Then it got sat on a shelf. Then I went to sell it but the guy didn't want it so I takes it home and figured hell I'll just use it a little bit and we were back to no boot. Must be a bad mobo, found it is an elcheapo and they way too much, it was a Dell and has an ECS I think mobo in it and I am not paying $60 for an outdated board.

But I think you are down to the BIOS, or a bad mobo or processor.