Stop sound playing over the top of itself

Okay, i really need some help on this. I have a play button where if clicked will play the sound over the top of it when its already playing, if that makes any sense. the sound is already called on the first frame. if the user clicks the play button again, it will play over it.

heres my play button code. i need to know what to add to add to make it check to see if the audio is already playing. My audio sound is named myMusc.

on (press) {
if (playing != true) {
if (paused != true) {
playing = true;
paused = false;
stopped = false;
myMusic.start(0, 999);
}
if (paused == true) {
playing = true;
paused = false;
stopped = false;
myMusic.start(myMusicPosition, 0);
_root.myMusic.onSoundComplete = function() {
myMusic.start();
};
}
}
}

Thanks