Just try and reset the bios by clearing the CMOS memory.
This can be done in one of two ways:
Either take out the round battery on the motherboard for a few hours
Or 2, check the motherboard manual for something called a CMOS Memory Clearing Header. Its this jumper which you change (it can be near or a bit away from the battery, but sticks up) and when you change the position of it (from 1 to 3 for example), it resets it almost straight away. You then just place the jumper back and start up.
Try these two options. This will reset it, undoing any harmful changes you might have done
Hope this helps