How do I fix my iMovie?

I was in the middle of editing, and a pop-up window appeared with it's only option being a "quit" button. I clicked quit and reopened iMovie. All projects and events were gone. I tried to create a new project and an error window comes up saying "the operation could not be completed. no other information is available about the problem." I closed it and reopened it. I updated it. I restarted my computer. I deleted the app and downloaded it again. No luck. I've been using the app for about 7 months now and haven't had any problems. Please help ASAP.