I have used Movie Maker for the first time and thought it was quite impressive..........until I try to play back what I have saved!

One minute, it plays as I saved it, then I went to show it (IN PUBLIC!) and it had no sound :-( Then I tried it again and it played, but played the music file over the top of all my video clips so you couldnt hear them. 

I closed it down, then tried again and it was fine!

Why does it do this? I am so frustrated and worried that when I come to play it for real it will let me down! I am making no changes to it, but it just seems to do what it wants to do and I am just taking pot luck as to whether it will work or not!

Please Help, I only have until Friday and have been working on it for 2 weeks!