Windows Movie Maker lost clips

I am using Windows Movie Maker with my Windows 8.1 operating system. I was able to make the wlmp file including titles and video clips and sound. I was able to convert that to mp4 format and show the final product. But twice now, when I have gone back to pull up the wlmp file to make an edit, the video clips were gone. The titles were there, but no video. It has taken me a long time to put this together, twice. Is there any way I can recover the video clips in the wlmp file? Why were they lost? As a possible hint, there were times when I was dragging video clips around in the wlmp phase when my video clips went blank and I recovered by exiting without saving and thereby getting my file back. Also another hint, there were times when I put a clip on the desktop and when I later deleted it from the desktop the images were also deleted in the wlmp file. I have checked the recycle bin with no luck. I have the final mp4 product but have no way of making edits again without starting from scratch. Any ideas?