When I used my pc a few hours ago, nothing was wrong. But when I came back from a friend and restarted it, this happened:
It does still work, tough it has rebooted twice giving me a blue screen. The big black squares flicker, the blue and the yellow ones usually stay still.
I have updated the drivers witch does not really help a lot as you may see.
I'm using an unchanged Radeon 7800 with Windows 8. I have used this setup for weeks without any problems.