imovie '08 is not playing back audio incorporated into video

Okay. I am doing a Let's Play and using iMovie to edit my game footage and commentary together. However, I recently discovered that my game footage wasn't playing back within iMovie (the finished product exported and the base footage were just fine) And, in my most recent episode editing session, I found it would no longer display the movie thumbnails except for whatever one I had my mouse over... some help would be nice....