iMovie suddenly stop letting me playback and edit my projects.

I am using iMovie '09 version 8.0.6, I had no issues with it prior to today, but then all of the sudden it would shut down periodically and now I am unable to playback or edit any projects that I start. I have since deleted the projects and tried creating new ones, but it still won't let me edit nor will it let me playback video; I only get audio playing back, however, it now let's me play back audio and video by using the full screen playback. Why is this happening and can I fix it?