What player are you using? You might need codecs, there are a few links here
http://www.gnutellaforums.com/showth...ght=wmp+codecs

There's also a link to VLC player, which is pretty good & has lots of codecs. If you want to use VLC or are already using it, you'll have to preview & launch videos outside of LW (if you're using Win. Mac users can preview & launch within LW).