iMovie hangs when I launch the application

I was importing a movie from my camcorder to iMovie and it was working okay but unfortunately my son touched one of the camcorder buttons and so I had to stop the import because I do not know what exactly he did. I closed out of iMovie and relaunched the application. Now it just hangs.

How do I troubleshoot this? I've rebooted the machine and have tried relaunching iMovie and it is still hanging.

Thanks