Turn off the PSU then click the power button to use up any electricity left. Then either connect ( with a screwdriver, anything made of steel ) the 2 pins labeled as CLR_CMOS or remove the CMOS battery. If you go the pins way then remember to keep them connected for a few seconds to be sure that you cleared CMOS. Both the pins and battery are just under the blue PCI-E slot ( for more info, they should be described in the manual ).
This way you'll have your bios reset to default. Hope this helps!