Vista - Movie Maker won't play

I've recently been trying to make a movie on Vista's movie maker, but about a half an hour into the process, the play button freezes. I'm not able to play the movie I was just seconds ago editing, so I'm not able to see how it runs in order to edit more accurately. This has happened many times, and I find it very frustrating, considering I love to make movies. Can anybody tell me why this happens, or give me an explanation on how to fix this problem? Thanks!

I am trying to use my Windows Movie Maker and it keeps telling me that "Another User is using this program on this computer. Please close the other session of windows movie maker before starting back windows movie maker."

Can some body please help with this problem. I would like to know how to fix this problem step by step please.

I would be very grateful if somebody could help me.

thank u.