See what others think at http://www.google.com/search?hl=en&q=Win+Movie+Maker+won%27t+open&btnG=Google+Search&aq=f&oq=
I was using it to convert some AVI clips to wmv, and noticed the clip I was working on was out of synch. So I closed WMM and checked the file on the media player (it was fine).
it's always been glitchy, sometimes it'll suddenly close when importing, or freeze when rendering to files and I'll use the task manager to close it.
But now it won't open at all