The most common reason for the movies not starting is that you're connecting to our site with a slow internet connection. If you want to stream our movies online you need to have a fast internet connection! We recommend that you save the files directly to your computer before you try to play them. What you should do is right click on the Download links and choose "Save target as.." then choose where on your hard disk you want to save the movie, then it will start downloading :-) If you click a link directly it will try to start streaming but if your internet connection is too slow it will keep starting and stopping until the movie is entirely loaded and by then you could have downloaded instead and it would be available for instant playback whenever you wanted to view it.
This is sadly one of the few downsides to the new broadband age because movies in the high quality do require a fast connection.