@Jeff - I can't recall doing anything before it started. I installed a game not all that long before, but it was a game I'd already had and uninstalled. It didn't affect anything before. In addition, I watched things on Winamp through my TV after installing the game without any problem.
As far as the Winamp thing goes, I installed ffdshow, after the problem began, and it did nothing to help. VLC still does the blocky thing with certain shows. Futurama, for example, freezes constantly. When I watch Ranma, however, it is fine. They're all avi files.
@goat: I have the newest version, and I tried changing the settings and things stayed exactly the same.