Re: Need help ASAP, please
It's strongly suspect that the power supply is the issue, not the video card at this point. That span of time is still pretty small, so it's entirely likely that the PSU decided that it can't handle the needs of the video card and the rest of the system.
I would borrow or buy a new, higher wattage unit and see if the problem goes away. If it doesn't, then try the drivers. Even as it stands, the stock 480w unit that shipped in your PC, Plurality, is probably just barely cutting it. It's definitely time to upgrade to something with more juice. 750 watts is overkill for that system. 600-650 should be plenty and still have some headroom, if you're looking to keep costs down.