Problem playing lots of video files...

I have problems playing many video files, namely avi files, but not exclusively. The error Windows Media player gives is 80040265. It says the file is corrupt or not supported. I know for a fact these videos are not corrupt.

I've updated windows, updated windows media player, downloaded the latest divx and xvid codecs, installed defiler pak, and tried tons of different media players including VLC. They still won't play.

The only thing that I can think of is there's something in my system that is just screwing everything up. The only thing left for me to do is to reinstall windows.

This has only been happening since I installed Windows XP a few months ago.

Does anyone know what to do? It's really starting to make me mad. Thanks a lot.