Imovie Sound


I have OSX 10.2.8 and iMovie 2.1.2 I
I use an iMic to record audio input.
Using Final Vinyl when I monitor the input it's fine, when I play it back it's fine.
When I try to capture audio in iMovie it appears to record but when I play it back there's no sound.
all my existing movies have also lost the sound and when I import new video, although the sound is there on input, it isn't there when I play it back in iMovie. Aaarrggh!!!