AVI files leave a black box on the screen

Has anyone else encountered this and if so, come up with a fix for it? Everytime I play a AVI file that I imported to WLPG, it leaves a black box on the screen until I close the application out. I can still click on photo thumbnails that are underneath the box though.

This doesnt happen with .mov or mp4 files, though. I have tried everything I can think of (uninstalling all codecs, switching to a different codec pack, uninstalling and reinstalling WLPG as an admin, etc.) but I cant figure it out and it's driving me up a wall. It sucks cause this problem only affects my desktop running home premium, and not my other vista machines. Restore points are out of the question since I have no idea when the problem begain exactly. Not sure if it's worth mentioning, but the problem does not occur in regular photo gallery, or in any other program.

Any answers would be greatly appreciated. My vista machine perform flawlessly, but this little problem has been like a grain of sand in my eye lol.

Here are the specs on the desktop:

AMD 3500+
2gb ram
256mb ATI Radeon 2400HD pro