Black screen & no sound when playing movies / TV series in iTunes

I'm running the latest version of iTunes and OS X - when I try to play movies or TV episodes I've purchsed in iTunes and downloaded onto my MacBook Pro I am greeted by a black screen with the player controls showing along with a time bar which indicates that the item is playing - however the screen is black and blank and there is no sound. The MacBook is authorised in iTunes.

I can download the same items to an iPad and watch them on that with no problems.

I have previously had no issues with playing downloaded movies and TV series on this machine?

Thoughts?