Interesting problem I've got going on - I have a Biostar TZ77B motherboard. This morning I awoke to a computer that POSTed successfully but wouldn't display anything on screen. I finally removed my EVGA GeForce 8800 GTS card and the display output shifted to the on board video. Once there, I could see a "CMOS Failure" message. Changing a BIOS setting cleared the message (basically just 'save and restart').
I figured my GFX card had died so I'd live with on board video for a few days. However, now running on on-board video - when Windows puts the monitor to sleep (power saving), the monitor won't wake up. After a hard reboot I get the CMOS failure message again!
I don't get the CMOS failure message after every reboot or after leaving the system off - there seems to be some mysterious correlation between display and CMOS failure. I'm not even certain at this point if my GFX card has truly failed or not - windows can recognize it just fine (when I'm leveraging the on board video to actually see an output:) but nothing comes to the monitor when I display it as primary.
Pretty odd - any ideas? I'm going to swap the CMOS battery now out of curiosity.