Press the CMOS clear button while the system is off. See if that allows default settings to return and work normally. If that doesn't work, turn the system off and press the CMOS clear button for 5 seconds then remove the CMOS battery for 5 minutes. While the battery is out, press the chassis power button. The goal here is draining all residual power from capacitors. Reinstall the CMOS battery. The system should be reset to default settings and hopefully, if the failed overclock didn't destroy things, work normally.