Windows MovieMaker sometimes messes up when I try to split a clip: the timeline goes blank and vid does not split. What can I do?

I'm working on a big project and so far WMM is the only program that seems to suit my abilities and needs, but it keeps messing up. Sometimes it seizes up when I try to edit the amount of time an image displays. At other times I try to split a video clip but instead of splitting the timeline/thumbnails on the right of the screen just turn blank, and when I scroll down more lines of thumbnails also go blank, though the video still plays. This is very frustrating, it has happened several times, even after I went to "Uninstall programs" and told Windows Essentials to repair all components. Please help!