iMovie problem

I have to do this video project and I used Photobooth with the Macbook iSight to record it and I edited it with iMovie, but right as I was about to finish editing the last scenes, iMovie stopped playing sound. If I slowly scroll or hover over the video frames it will play the audio, but not then the video is being played.
What happened?
Oh, and the audio wave button is on, but the green audio bars won't even display while the video is playing, but will when I'm hovering over video layers.

 

Nevermind, I restarted iMovie and it worked fine.