on (release) {
music = new Sound();
music.attachSound("mix1");
music.start(0, 999999);
// set the volume of the sound to zero
music.setVolume(0);
// set a variable named 'vol'
vol = 0;
// set another variable named 'fade', putting a setInterval function in it
fade = setInterval(fadeIn, 100);
// set the initial fade in function
function fadeIn() {
  // fade the sound in with an increment of 3 in the variable 'vol'
  vol += 3;
  music.setVolume(vol);
  // put an if condition to restrict the increment in volume after it reaches to 100
  if (vol>=100) {
  clearInterval(fade);
  // create the 'step' variable
  step = 1;
  // create the 'fade' variable
  Fade = 0;
  }
}
// create the fade in and out function
// function executed on onEnterFrame
_root.onEnterFrame = function() {
  // set fade out
  if (Fade == 1) {
  vol = vol-step;
  if (vol<0) {
    vol = 0;
  }
  music.setVolume(vol);
  // set fade in
  } else {
  vol = vol+step;
  if (vol>100) {
    vol = 100;
  }
  music.setVolume(vol);
  }
};
}

u mean..
when the movie play.. the music is off.. then click to turn on the music...
after the music played.... we cant click the button nemore???

on (release){ play_btn.enabled = false;}