I've noticed that since I've been reassembling the Videos portion of this site sometimes the media player doesn't open even though the music of the video begins.  If this is the case (and until I get this fixed) the solution is to open the media window.  It will already be activated with the video, but needs to be opened to the desktop to see it.  If the media player window opens but only as a smaller window on the desktop, simply expand it as you would any window.  You can also select double-click within the window and that should take it to full screen mode.  To exit full screen mode click the Esc key.