Bump!
I've been having the same problem for a while now, a little worse than everyone else though.
My card is an XFX 256mb 6800GT (AGP). I'll try to dig up some details later.
This started a few weeks ago, around the time I got a new monitor.
Recently my CRT had broken, so I had been using the TV as a monitor for a few days, my new LCD eventualy arrived, and after a few days, (just before I went away for two weeks), it started screwing up. Random colours, PC eventualy rebooting, etc.
After I came back, it was fine. I was happy that the problem was gone, then in the middle of a game, boom, there it was. Now it happens before I can even log in, sometimes after I reboot, it fails to output any video as soon as it begins to load XP.
But one interesting thing I think I've found out, is that it seems to be ok when running without any drivers. It's 100% fine in safe mode, and if I uninstall the nVidia display drivers, and boot up normally, it seems to be ok. But recently I think that also failed, but that would be the first time.
I've tried older drivers from the XFX website, no change. I've removed all nVidia drivers, motherboard drivers, run driver cleaner, then installed them all again, nothing.
I'm now using my other graphics card, with the latest drivers from nVidia, no problems whatsoever.
A little after this began, I realised that I had actualy made a hardware change around the time this started happening. I had three sticks of RAM inside my PC at the time, 2x256mb, and one 512mb. It had always displayed 768mb of RAM, and I couldn't understand it, but when my computer was in the living room hooked up to the TV, I noticed that one stick of RAM wasn't fully slotted in, I slotted it in, no problems. One thing I found odd, was that BIOS was telling me that dual channel was enabled. If my memory serves me, this can only work when two similar/exact sticks of RAM are inserted, not three, where one is different to the other two?
Either way, I took out the third stick, and I still have the problems.
Has anyone found a way around this other than an RMA?