There are a ton of video tools out there. First try Virtual Dub at
http://www.virtualdub.org/
It may take you a minute or two to figure out how to use it, but it is free. Click the box "Ask for extended options" when you are opening the file.
If that doesn't work you may want to try a commercial tool ... they usually cost in the neighborhood of $30 though. Google "AVI repair".