Try resetting your CMOS.

Turn off the machine and unplug the PSU.
On the motherboard there should be a 3 pin header for the CMOS with a jumper spanning 2 pins.
Lift the jumper off the 2 pins and move it along 1 pin to short it out.After a few seconds put the jumper back into its original position.

if the pins are theoretically numbered 1 ,2 ,3 the jumper will be on 1 & 2 . Remove the jumper and re-position it onto 2 & 3. After a few seconds put the jumper back into its original position.