Thanks for visiting Apple Support Communities.
You may want to remove the episodes from your computer and download them again using the steps in this article:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
Additionally, this article has some troubleshooting steps to try:
Troubleshooting iTunes for Windows Vista or Windows 7 video playback performance issues
If the issues persist, see this article for the steps to report an issue with your purchase:
How to report an issue with your iTunes Store, App Store, Mac App Store, or iBooks Store purchase