If the video card failed, you could try removing the video card and seeing if you get a breaking glass sound. If this occurs, then good news: add VRAM, it was a bad card. If it doesn't, this doesn't necessarily mean you're hosed, though.

That said, I haven't heard of that sort of failure much.

Your other thing to do is reset the CUDA. I don't remember where this is on the 8500, but it looks like a little push button marked "CUDA RESET". If that doesn't work, unplug the unit, pull the PRAM battery, press the main power button, and let it sit for at least 10 minutes.