Have you tried resetting the BIOS to defaults? A quick google search turned up this mention of the same problem:
Looks like possible BIOS corruption. "AA" stands for Altered Assembly, reffering to when a motherboard is 'altered' by a third party and resold (afaik). For example Intel makes the board, and it might later be altered and resold by Dell. If there is any warranty left you should see about getting an RMA. Other than that, I would see if there is a BIOS update or fix on the manufacturer's website. Be careful though - if the BIOS is indeed corrupt, updating may cause it to fail completely. If you're not running with a keyboard all the time, I might suggest leaving well enough alone.
Hope this helps, Good Luck.