If you see a green screen when you try to play a video, you probably need to install the latest QuickTime upgrade. You can download QuickTime free of charge from the Apple website at:
You will need to restart your Mac after upgrading QuickTime.
If you are attempting to view your video on a Windows computer, I recommend the following articles:
Troubleshooting iTunes for Windows XP and 2000 video playback performance issues
Troubleshooting iTunes for Windows Vista or Windows 7 video playback performance issues