Movie maker freezing up during project

I have Windows 8 and use Movie maker at least once a week...until tonight. I've got my project up - photos and music and everything was going along perfectly until I was nearly complete and tried playing it back. I noticed that some images that I could see on the right, wouldn't show up in the playback area on the left. I removed those images and began replacing the duds, then everything stopped working. It wont play or let me add transitions - I can't even save the project.  Nothing is working. It's the second time tonight that I've had to start this project over again due to this. It's never happened before. Any suggestions?