[F8] logic script for sound play button, please help m(_ _)m

now i need senior help with logic script, first sorry if i asking newbie question, but i am really sucks on proggraming, so please help me

on (release) {
my_sound.start(mmpos/1000);
my_sound.onSoundComplete = function() {
my_sound.setVolume(20);
my_sound.start(0, 999);
}
}

here my play button
i make the button looping because the sound placed on a frame
<due preloader problem, i need to place sound on a frame, i got the tutorial from http://actionscripts.org/tutorials/intermediate/sounds_and_preloaders/index.shtml>

current this play button keep starting new sound even the first sound haven’t complete [stacking], so i want to make the play button ignore play if the sound is on

if my_sound = on
then do nothing … something like that ^^

please help me ^^;
thank you very much!!