I have a GeForce 8800 GTS on my machine which i'm pretty sure is dead - or at least part of it. I'm still getting output to my monitor, but as far as gaming (WOW) or even accessing the vNidia control panel goes, i'm out of luck. The card no longer registers on my system - my display adapter tells me: "Windows has stopped this device because it has reported problems. (Code 43)" and when i attempt to access the nVidia control panel, it tells me: "You are not currently using a display attached to an NVIDIA GPU."
So is this indicating that I still have basic display function capability with the card, but not the GPU portion which is needed for gaming?
It is likely using the default windows VGA drivers. They will be ok for basic functions but not much else. Have you tried reinstalling your Nvidia drivers? Uninstall them and run driver sweeper in safe mode; http://www.guru3d.com/category/driversweeper/
Then get the latest drivers from Nvidia; http://www.nvidia.com/Download/index.aspx?lang=en-us
If that doesn't fix the problem then you are probably right about the card dying. If you want suggestions for a replacement tell us about your system, power supply, native resolution and budget.