1) What media player are you using? WMP 6.4?
2) Is there any sort of information showing up in the text area of your media player display when you first start the video? like "failed to download codec" or something?
Sounds like you may need to install a codec to get the video to show up. Go to http://www.divx.com/
and download the latest freeware bundle of their codec & player.
Still doesn't work? Download the XviD codec, and/or ffdshow and install those. (use Google to find them)
If you see the windows desktop on your TV, but a blank window and sound only in your media player window, its probably codec you need.