Have you added any new hardware? Did you attempt to do any changes in the bios before this problem happened? You do not leave to leave the power cord disconnected to effect a change. Try this to clear the bios next time. Turn off computer.......disconnect power cord....... remove cmos battery. Wait approx one minute......reinstall battery...... connect power cord and turn the system back on. We will pick back up from there and after you answer the above questions.