Video Problem

I created a small video using Windows Movie Maker. I got an iPhone the other
day and installed iTunes. After installing iTunes and the recent round of
Windows updates (Vista), the video I created does not play smoothly. It is
jerky and slow and actually only plays the first few seconds (Media Player
Classic). When I try and play the video in Windows Media Player it doesn't
play at all. I get this error message, "Windows Media Player cannot access
the file. The file might be in use, you might not have access to the computer
where the file is stored, or your proxy settings might not be correct." I
tried the video on another computer and it plays fine on it. When I open
Windows Movie Maker it won't play through the storyboard images at all. So
whatever is affecting the small video (AVI) is also affecting Windows Movie
Maker. Also many other AVI's that contain sound don't have any sound when
they play, however they do play at the correct speeds and are fluid.

I tried uninstalling iTunes, I tried the iTunes patch, I uninstalled all the
updates, and I tried to use a Restore point, nothing worked. When I try the
Restore point it gets all the way through the restart and then it tells me
that it didn't function and no files were altered.

PLEASE HELP!!! I have to have the video playing for an upcoming event. It
is CRITICAL!!!