It sounds like you are having some audio issues and the video is out of sync. I recommend these steps from either of these articles depending on your OS version:
Troubleshooting iTunes for Windows Vista or Windows 7 video playback performance issues
iTunes for Windows XP: Troubleshooting video playback
If these do not resolve the issue you are having, I would next delete the video:
Before you delete, find out if you'll be able to download the movie you deleted again (it depends on where you live).
- Launch iTunes.
- From the Library pop-up menu, choose Movies.
- Click Movies in the navigation bar.
- Click the movie you want to delete.
- Press the Delete key on your keyboard.
In iTunes 11, the movie cover art will remain visible, but a cloud icon will appear on it to allow you to download the item again (in countries that support this).
From: How to delete content you've downloaded from the iTunes Store, App Store, iBooks Store, or Mac App Store
And use the following article to download it again:
iTunes 11 for Windows: Download previous purchases from the iTunes Store
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