One Last GUI Question

So I been working on this script for a little bit now. I finally got it to work right which I’m happy about. I added a little bit to it and theres no errors but I have a problem. See the thing is when I start the game Screen.LockCursor = true which I like. And I added that into the script. And I added when you open the menu Screen.LockCursor = false and that works. But my problem is when I close the menu Screen.LockCursor still is false. Can you help out?

var GUIon:boolean;
function Start(){
    GUIon = false;
    Screen.lockCursor = true;
}

function Update(){
    if(Input.GetButtonDown("Menu"))GUIon=!GUIon;
}
function OnGUI(){

   if(GUIon){
      Screen.lockCursor = false;
      GUI.Box (Rect (0,0,500,300), "FOV");

      if (GUI.Button (Rect (20,20,80,80), "FOV = 70")) {
        Camera.main.fieldOfView = 70;
      }else if (GUI.Button (Rect (100,20,80,80), "FOV = 80")) {
        Camera.main.fieldOfView = 80; 
      }else if (GUI.Button (Rect (180,20,80,80), "FOV = 90")) {
        Camera.main.fieldOfView = 90; 
      }
   }
}

Since UnityAnswers’ indentation is horrible, I’ve posted it here: var GUIon:boolean;function Start(){ GUIon = false; Screen.lockCursor = - Pastebin.com