Do you mean that you can download video files, but when you play them there's sound but no picture on the screen?

You might need codecs for your player. This thread has links to lots of codec packs. There's also a link to VLC player, which is free & has codecs installed to play most files. It's a good player
CODECs list for Movies/Audio/ Alternate players / Video help forums/ video-mp3 fixers


Or, do you mean that you can download music files, but can't download video files? If that's the case, you're most likely seeing fake files. Try the tips in the thread below.
http://www.gnutellaforums.com/downlo...tml#post297713