Well if you are trying to watch them with Windows media player, and get sound but not video. You probaly need to download the divx codec
http://www.divx-digest.com/software/divxcodec4.html divx 4.1, I think is the best for encoding and decoding. I had this same problem in WinXP. It would say trying to download the needed codec while trying to play the clip, but then windows media player would pop up a box saying it could not run it. After I installed divx4.1 all is good. And thats what I use for encoding video for my Ax to...Hope this helps yah..