Help with GUI clicking ???

Hi guys i just wrote a script which plays a song when the GUI is clicked. The problem that i am having is that when i click the GUI button again it plays the song again and it starts to overlap the song that is playing and it sounds horrible. Now what i want to do is if the song is playing and the GUI button is clicked again i dont want it to play the song again if its playing.

here is the script that i wrote:

 var MyAudio : AudioClip;
  function OnGUI () 

 if (GUI.Button (Rect(10, 20,105,20),  "Play Track 1 ( Enter) ")){



thanks in advance :)

You could use:

if (!audio.isPlaying){
  audio.clip = MyAudio;