I don't think it will be that, but you could try it i guess.
Either take the battery out for a few hours, or if theres a bios cmos jumper, move this to another setting to wipe it, like if its on setting 3, take it down to 1 for a few mins, then put it back.
This isn't neccessarily near the battery as it can be at the bottom of the board in some motherboards. heres a pic:
It should have at the bottom in small lettering, CMOS memory header
I hope this helps. You did say you've tried a reformat?