You might need codecs for your player? You'll find links to codecs within the thread below & also a link to the free VLC player, which has codecs installed & plays most file types. Download from the nearest mirror site.
Codecs & VLC

If you do decide to try VLC, you won't be able to preview or launch within LW. Go to LW library, click on Incomplete Files then explore...the folder opens outside of LW & you can preview from there.
Same deal for launching completed downloads, except you'll click on Saved Files then Explore & launch from there