I am working in iMovie '09 on a pretty new iMac running 10.6.7. I am working on a project, some clips of my son playing football. Everything was fine until I converted a short clip in order to apply a slow motion effect. Now there is no video on playback, just a green screen. (Audio is fine.) Whether I try and play the edited clips in the project, or the clips in the library, there's no video -- just a green screen. In fact, whatever frame the cursor stops on will turn green while the other frames remain normal. What the **** is going on??? Please help!!