For what it's worth, I'd say you have a problem with your video card.
Are you using the NVIDIA GeForce 9500GT 285.62 driver by any chance?
If so, you may want to revert to the 280.26 version as the 285.62 driver has known black screen issues.
I know this to be true because when I installed it I got a black screen (i.e. no video, sound was OK) when using the Windows Media Center.
When I rolled back to the previous version (280.26) the problem was solved.