I have just purchased a full version of Movie maker 2012

I have used another copy of the software which I have now unfortunately deleted and have had no problem in editing video clips without effecting the quality.
Now when trying to use this new software ( Movie Maker 2012) , I load the Clip or Clips which are in an MP4  format, the software wont allow me to edit the clips - IE - Insert an Title Page , Animations, Music or Captions.

The funny thing is that  before I start editing and that the raw video clip or clips are loaded the Movie Player will play the Clip or Clips with no deterioration in quality, but as soon as I attempt to edited it in any way the clips quality is lost

Please  can you help

Thanks Richard