I have this sapphire hd 6950 2gb for about 18 months and it just started doing this. Went into a game and got a black screen. System would not respond to Ctrl-Alt-Del, Atl-Tab, reset button or anything. Had to force power down. Had a mild overclock on, but now it's reset and still doing it. Tried a different game, 3dmark11, same thing. After a few minutes black screen. Going to reinstall catalyst, but I'm pretty sure something else is going on. GPU, PSU, memory, motherboard...don't know which. Any ideas would be appreciated. ADD: Forgot that I'm running a 4.8GHz overclock, so testing at default and so far looking good. Perhaps it wasn't as stable as I thought at that speed, but still not sure yet.