Maybe trying a different media player for a start.
Are you sure that the files are '0' KB (MB)? If they aren't and they won't play, you could try to use a different media player such as the free VLC player with built-in codecs which can play almost all media files without problems. You can downlaod it from here:
http://www.videolan.org/vlc/
As a side note, to preview files with it you'll have to open the files directly from the Incomplete folder and not via the LW preview function.
