Lost the weekend thinking I'd blown up my XPS video chip.
Update: It was nVIdia chip after all! Everything I said below ... all the wildly varying advice on the web and from our in-house tech ... was for naught. In fact (as some reported) the nVidia chip slowly fried into digital mush.
Lucky for me, Dell replaced the motherboard (at last that 3 year service agreement pays off!) and haven't seen any problems since. A BIOS update that turns on the fan at lower temperatures was also part of the deal. My XPS isn't as quiet any more but she's running!
I leave the completely false information below as a sign of the abounding misinformation. Do not be fooled and waste hours thinking you can fix this yourself or blame Microsoft.
--- The following is false ---
Turns out Windows Update automatically replaced my Vista nVidia driver with something Microsoft recommended. Their replacement driver behaved in ways that looked like hardware failure to me. Rolling back the driver didn't help which made me "sure of it".
I'm way out of my league with this stuff. Thank goodness we have someone on staff who could figure it out. The clue that it wasn't hardware is that everything worked fine (if ugly) running with just VGA drivers. Like I know how to do that? No way. But my guru did. Found the correct drivers on Dell's site and reinstalled them.
I don't know how the "normal" world copes with this stuff. One minute everything is fine. Next minute (after a Windows Update that you didn't even remember seeing), your laptop is failing with bizarre video artifacts, driver reboots, freezes ... and you're weeping like a baby.
- Don't let Windows update your machine without your explicit agreement
- Don't download the optional stuff
- Examine the proposed updates carefully and choose the ones you "know" to be safe. My guru advises that I stick to the security updates only.