I am using the trial version of Windows Movie Maker and produced a short video,which plays okay with transitions etc and looks good. problem is when I try to add Music. I click on the add music icon which brings up music files on PC

I choose and open a track, its loads under the video clips as it should but as a solid short line not sound waves, the sound adjustment window panel "fade in-fade out" duration etc is grayed out.  Video plays fine but no sound. Is it a Codec problem? if so how do I resolve it and load the correct Codec. PC is 64bit Desktop

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