Help with video editing

[Dimmerswitch]

I am new to editing .3gp videos. I have windows 7 os, and windows live movie maker. Android plays the videos with sound, but Windows media player plays the videos without audio. I can't find any sound track on Movie maker. There are no codec's (whatever that is) listed on the properties window for the file.

What I want to do is replace the original sound with music and shorten the video.

Any ideas?