Latest itunes wont play any of my purchased content, neither does quicktime, what do i do!?

Everytime i try to play a purchased movie or tv show on my itunes y just get a black screen,same on quicktime, tried all the authorizatiion fixes, downloaded itunes and latest version of quicktime, even downloaded an old version of quicktime to see if it would work, and nothing, WHAT DO I DO? im desperate, this problem has been going on for too long now and i just want to watch my movies!!!