I use Windows 7.  I downloaded Movie Maker as part of Essentials 2012 yesterday to create a short film from .mov files and photos with a recorded narration.  It was very easy to use and I created a film I was very happy with.  I could watch it / preview it in movie maker perfectly.  But when I tried to save it as a movie (in both .mp4 and .wmv formats), it appeared to work but then when I replayed it I had all the audio but no video (just a black screen).  This was exceptionally frustrating and I wasted hours of my life yesterday re-booting, re-trying and searching for online answers, all to no avail.  I also created other projects with just one movie clip in them, and tried a range of different formats for the original file (.avi, .wmv, .mov etc), and they all had the same problem. There is clearly something wrong with the "save" option.  I don't have any problem watching movies on my laptop normally.

I need specific advice please - e.g. being told I have a codec missing, but not which one is not going to be any use !    

Thanks