Not often, but every once in a while, when I'm working on a project in Windows Movie Maker - especially if I've been working on it for a long time - the preview screen will go black and the timeline will refuse to play. This means the project has become corrupted. Sometimes it happens when I'm in the middle of an editing session, and that's when it's most irritating. I don't even know why it happens at all.
So far, though, there's always been a way to save it.
The first thing I do is copy all the project media in the timeline and paste it into a new project, one track at a time. The new project should work.
If it doesn't work, I delete some of the media. For some reason, a project being too long can eventually cause corruption. Sometimes just deleting one big clip fixes it.
If you need part of the clip for the video, you can either delete something else or try copying and pasting the clip you need into another project, cutting out the part(s) you don't need, then copying the part(s) you do need and pasting them back into the original project.
Corrupted projects are very tricky and I don't know any other methods of recovering them, but those two work for me.
