well theres somthing wrong with either your LW, media player or the file types assisiation, cos preview is an indespesable part of fileshare i cannot imagin how imposible it would b with out preview, even 4 music let alone video.

try a reinstalation of LW and also make sure that your video file format has a working assotiation i.e when you open any video files that you already have, that they open either windows media player or real player, not sure if having any other media player associated with your vid files will load when useing LW, prob r but i never used any others.