Hrm.... I can give a couple of thoughts before you go out and get a new card.
Got another PC? Try the card in there, if so.
In safe mode, go to device manager and delete the video card and reboot.
IMO, if you POST, you get safe mode, etc, it might be corrupt drivers, but the card seems to work.
Windows desktop takes precious little resources to display on a vid card. It shouldn't do that. If the card were partially fried (and it still does safe mode and POST so it's not totally fried) I'd think it would display SOMETHING in windows, but perhaps be corrupted, or show artifacts.
Also when booting up try the "last safe configuration" or whatever it's called.
Try removing the device in device manager first, then windows should boot up normally and re-install it.