Why can't I hear my music on my Zen Micro when It shows that it is playing?

I have a Zen Micro MP3 player. It shows that the music is playing but I can only hear the music out of one earphone. I have tried moving the plug around and pressing on it, it worked for awhile now it barely works at all. It seems to all stem from the headphone jack.
HELP PLEASE
Rachel101, June 2009