Movie Maker missing images and black. just started.

I've been running Movie maker on Windows 7 Ultimate without problems for a while now.  I have many videos in my library. when I recently went to edit some of these, I found missing files and the entire video strip is black.  I have sound.

On one video I could see the images on the strip but they would not play.

I've got a lot of work to do so would really appreciate an answer. Also am hoping the information is not lost.

Thanks