Are you getting any error messages when you try to play vids?
Try playing with VLC player. It's free & has codecs installed, plays most things. Download from the nearest mirror site.
http://www.videolan.org/vlc/

When you go to launch, don't do it from within the LW library. Within the library, click on Saved Files then click Explore. Your saved folder will open & you can launch from there. The same applies for previewing, except that you'll need to click on Incompletes to open that folder for previewing.