Shutdown PC and unplug power from PSU.
Pull the CMOS battery out for about a minute.
If there is a CMOS clear jumper, move it over, wait 30 seconds.
Put CMOS batter back, return CMOS jumper, turn on.
Everything should be reset to either factory default settings, or the default settings of the last BIOS update, if you did one.
If not, is there an option in BIOS to load BIOS from USB?
What about from drivers disc?