To get some movies to play you must download the codec pack
You must download it and install it has important codec’s for movies players, included in the codec pack is a basic media player however this player will play 99% of the movies online.
As the movies are posted by other people we don’t have much control over them.
If you are still having problems after this try updating you graphics card driver.
Problems after this could be hardware related IE ram / cpu cannot cope although this would probably only occur in machines older than 3 years.