I am a ME user that has had the same problem in the past, and this is the solution that worked for me.
If the video’s you are talking about are the AVI file type then you need to run get and run a small program called “DivX 3.11 alpha”.
Here are two places to get it:
http://www.doom9.org/software2.htm#codecs http://www.dreamytimes.com/codecs/moviehelp.html
The Doom9 site has some newer versions, but try the “DivX 3.11 alpha” first.