Won't allow me to access my project.

I'm editing my media project on the latest version of iMovie, and everything started going wrong. First it shut down on me with no warning, but when i accessed it again it worked fine for a while. Then it started saying that the source clips weren't available, although they were still in my event library, and wouldn't play back. It kept freezing - only playing the audio of my project rather than the video. Then the source clip warning went away and it carried on working although it froze every so often and was working slowly. Then it stopped playing back altogether, the playback screen froze and i could only hear the audio. But then i changed the name in the Project Library and it included a full stop, and after that i haven't been able to access it. On right click the only option i have is 'full screen play back mode', and when i do this the screen goes black with the loading symbol in the middle, and the only way to escape this is to force shut down. Help?!