Increase sound button code

programming flash
1

I made a button that starts the song, but when you press on the same button again it starts the song a second time. So now it is playing twice. Could use some help so no many how times the button is pressed the song only plays the first time it was pressed.

var song:Sound = new Sound();
song.attachSound(“Transylvania.mp3”);

var upVolume:Number;
upVolume =5;

this.sound_ro.onPress = function() {
song.start(0,10);
song.setVolume(upVolume);
sound_mc.gotoAndPlay(“rollout”);
sound_an.gotoAndPlay(“rollout”);

};