I had this problem recently and I finally, after some research and testing on another motherboard, come to the conclusion that the BIOS is corrupt. I found that other than getting a new board all together that you can download the updated BIOS and try to boot directly from that or you can (this is MUCH more risky and would really not suggest it) take a CMOS chip from another board and put it in your faulty one and boot from that and while the computer is running switch the CMOS with the original and flash your BIOS.

Thanks for that, it certainly got me thinking. My BIOS chip is mounted in a socket and for £12.49 plus shipping I can replace it with a new one pre-flashed up-to-date. I'm not sure where you go in the US but here they can be purchased online from bios-repair.co.uk | Flash BIOS Repair | Flash BIOS Replacement.
I will let you know if this fixes the problem, otherwise its a new motherboard.
Goodness knows why my BIOS decided to give up - its not as if I was flashing it or anything else.

Just to let you know that the new chip worked. Issue resolved.

Thanks for letting us know,i'm glad you got it fixed...