I noticed that video playback in vlc and the visualization in iTunes (if I use the default DX-version) doesn't work either. The workspace in photoshop has the same issue. Blender shows just a black windows. And the standard windows screensavers are just black, too.

So these problems are all related with graphics / directX, but I don't have the right idea how I can find the problems source. I've already reinstalled my gpu driver and DX 9.0c, but there must be still something different broken.

If you have any loose idea, what this could cause, please write it here - I don't wanna format the whole pc :'(
Scorpion