I has been working on a project for about 3 hours and I exited the project and then when into a few other projects. However, when I tried to go back into the project it wouldn't allow me to and the image also froze on the preview pane. I exited iMovie multiple times but the same thing kept happening when I opened it. I even tried to restart the computer but nothing's helped. What do I need to do to be able to open the project?