Trouble with video editing (basic)...

[MoleVision]

I've got a couple of videos from my mobile.3GP files that I've converted to a number of formats (.AVI .MOV .MP4) so I can edit them in windows live movie maker (I know, I know, not the most advanced piece of software - I only wanted to cut out sections to keep the good bits.)

However.. I seem to lose the sound when imported and exported after editing.


My question is.. why?
Or
What other (free) software is there that might give me more luck?

any ideas - done a google search but not come up with much?
Thanks