Interesting as I see the same issue, with same symptoms once or twice a game using the GTX260, Win7 32bit. The game is happily running even though the display has stopped, you can even exit cleanly and save your game so you don't loose any progress!
I've run in windowed mode and when it goes black I see a windows pop-up saying the NVidia display driver crashed and recovered. I wonder why, it doesn't happen predictably or at any obvious trigger.