I don't think you can open & play video files that are not being shared by LW for a start. The video files must be present within the Public or Private Shared of LW to be able to be launched & played by LW's media player.

For other video files on your computer, set either WMP or VLC as your default video player. VLC tends to be more reliable than WMP since VLC has all codecs built into the player itself .. VLC does not use external plug-in codecs.