I have seen different motherboards use F8, F5, Delete, and a couple others. You could try going to the manufactureres website and checking for a PDF manual. The info should be in there.
Edit: Another option is to pull the motherboard battery out for a couple minutes and then put it back in. That "should" reset the bios to all factory defaults. Or like my board, there is a button on the motherboard specifically for reseting all bios settings.