Itunes not loading movies.

So I had issues with iTunes movies having the sound go out of sync, and the only way to fix it was to un-install and re-install iTunes. It worked. Watched a full movie, and half of another-from the cloud since it's all gone form my computer now. Now wehn I go to watch a movie-well seems half of them won't load. It gets to the movie screen, and might play a 5-10 seconds, and that's it, just stops playing. Works fine on my iphone. Any help?