If you tried everything and didn't solve it, it's unsolvable. Then it's time for a new motherboard (allthough maybe you tried that also, you forgot to tell).

http://forums.cnet.com/7723-6121_102-522736/boot-up-fail-with-checking-nvram/ is a prior discussion about resetting the BIOS to its default state. But since that's the first thing anybody would do it's certainly included in your "everything".

Kees