Don't despair yet - try one more reset of the CMOS/RTC Ram:

To clear RTC, Turn OFF the PC and unplug the power cord. Press the power button. Being careful to discharge any static electricity from yourself, open the case and remove the CMOS battery. Set the CLRTC1 jumper cap from pins 2-3 (default) to 1-2 for 15 seconds and then return the cap to pins 2-3 and re-install the battery. start the PC and enter BIOS setup.

IF THAT FAILS, you could try a Bios Flash.