iMovie playback has suddenly stopped playing audio

Suddenly all my movies & projects do not have audio on playback. I can see there is audio on all, but once I hit the spacebar to play, iMovie shows it as no audio in the volume level window. I have iMovie 9.0.9 and Mac 10.7.5 I did what I usually do, imported the video from my Sony HDR-PJ260 and imported it into my MAC/IMOVIE, then made it into a project. Nothing differnt than what I have ever done before. Help??