Replying to New iTunes Problem

Ever since I downloaded iTunes 7.0, all the videos I have in my library won't play. The video window will pop up and I will hear the sound but all I am able to see are green and pick fuzzy lines. This is getting really irritating and I have checked the apple support site and their discussion forums and found nothing helpful. So the next step is to ask NS. Does anybody know what the problem is, or better yet, how to fix it? Thanks in advance.