Keep in mind LW's media player can only play audio files.

Sounds to me like you need to change the default for playing video files. See Setting Default video app

BTW if you're interested, a player called VLC - (click on link) _ (choose nearest mirror site) has in-built codecs & is generally very reliable. We frequently recommend it for people playing their videos.

Else make sure you have all necessary codecs for your normal video player, CODECs list and alternate players for Movies