Just follow these steps, if the issue is with Apple TV:
First, check if your Apple TV Software is updated:
1. From the main Apple TV menu, choose Settings > General > Update Software.
2. Follow the onscreen prompts to download and apply the Update.
3. When the Update has downloaded and finished installing, your Apple TV will restart.
Then check this article:
How to rent a movie from the iTunes Store on Apple TV
http://support.apple.com/kb/HT1498
If the issue is with your Apple ID/iTunes Store account..... contact iTunes Store Support @ http://www.apple.com/emea/support/itunes/contact.html