I recently set up a new machine, and everything worked fine after the fresh install, minus a few devices because the manufacturer didnt include Vista motherboard drivers. After the first round of updates, the Media Center application and any fullscreen multimedia applications (Media Player / Photo Slideshow) would not display anything. This had worked previously. The applications run, as there is sound and you can blindly click through menus, but the screen is black.
Thinking this might be an updated video driver from the MS site, i checked installed updates, but did not find any gpu specific update. I visited nVidia's website and installed the Vista drivers with zero luck. I found beta drivers on the site which allowed Media Player to finally play in fullscreen, but the photo slideshow and media center are still blank. I uninstalled those drivers and removed the video card from the device manager to hopefully force the windows default drivers that loaded just fine when i installed Vista, but that didnt work either. I went back to the semi-functional beta drivers from nVidia, and am stuck with limited functionality.