Video image split down the middle of screen

I was playing Homefront on my PC with a Radeon HD 6870 and all of a sudden the right edge of the screen was in the middle of the monitor and the other wrapped around the other side. Only a restart fixed the problem. What could cause this? Bad card? Drivers? Thanks.

Make sure your PSU has enough juice to properly run the card under heavy load. If push comes to shove, try a more powerful PSU in say a friend's PC. I'd also contact your card's manufacturer for support info. Maybe your card is duff and can be replaced. However do try one thing, plug your monitor's cable in to a different port if possible and make sure it's in properly.

Its a 1000W supply so I am sure its fine and it has never done it since, so I don't know what happned. Mabe the driver just crashed, it's a fairly new game so who knows. Just wanted to see what could have caused that. Never seen that happen and I have too many new things that could be the issue.