How old is your system, if over 3 years then I would try changing the CMOS battery.
This will Clear your CMOS also.
If relatively new then:
Have you tried clearing your CMOS. Normally there is a Jumper that you put on two pins for about 5 Min. NOTE: When you do this either turn the PSU Off (Rocker switch on back of computer, or Unplug the computer - I prefer the Turn PSU off and leave pluged in).