One thing you can do before assuming the worst is:
Check in your BIOS for a setting that allows to "reset configuration data" (turn it on, reboot)
After rebooting, go back into the bios and make sure everything is as they should be, reboot again, and if symptoms still occur , you're probably headed for some type of hardware error, whether or not it's the video card, I can't be sure, but gathering from your information, it seems most logical.
P.S. I have saved one system, in the past, which give very similar symptoms , by re-installing the bios (flash), everything was back to normal after that, and the card was fine. I'm not recommending you re flash your bios unless you know exactly what you're doing, and it should certainly be a last resort (I'd recommend replacing the card instead, especially if you don't have a backup system).