I recently bought a hd radeon 6850. It worked perfectly for a few weeks and then while just surfing the web I got a black screen. I didn't over clock or modify it in any way. The fan still spins so it's drawing power but the card doesn't show up in the device manager. Restarts do not help, still black. I attached the monitor to the old integrated card and I actually get some video again. I removed the 6850 drivers and reinstalled, but it still doesn't work. My psu is a corsair 600 watt. Has anyone heard of anything like this? Is my card just defective?