Just an update. We pulled the Radeon card (5700 series) as well, thinking to just replace it. Attached the monitor to the onboard video, installed windows 8, and now within 15 minutes we are getting the balck screen,. THIS time, however, windows 8 comes up and says we had a video_tdr_failure ....which google in dicates is a video hardware or driver issue (and again, the radeon card was removed, using onboard only, with FRESH windows 8!).
Motherboard issue?? Prior to the windows 8 install, we had disabled onboard video via the bios, and the pc ran fine for a year. I don't want to pay $200 to have dell re-support it, when it sounds like a major issue with this model.