Collision problem

I'm making a game to just try and learn the ropes of unity as I'm too good with it. I'm making a simple platformer with an up and down moving platform. However when I set the platform to start moving when the player collides with it, nothing happens. I know there's nothing wrong with my movement script as it works perfectly when I have it set to be on at the start.

If someone could look at my collision code and tell me why nothing's happening it would be appreciated.

 var speed : float;                //speed at which the platform moves
 var startOn : boolean;            //If the platform should move at the start
 var pause : float;                //How long it pauses for
 var onTime : float = 0.0;        //amount of time that the object will move before pausing
 var up : boolean;                //direction the platform moves in
 var target : Transform;            //What must collide with the platform for it to start moving
 
 function OnCollisionEnter (collision : Collision)
 {
 
     if (collision.gameObject == target)
     {
         if (startOn == false)
         {
         startOn = true;
         }
     }
     
 }
 
 function Movement () {
 
     var controller : CharacterController = GetComponent(CharacterController);
 
         if (up == true)
         {
             controller.Move(Vector3.up * speed * Time.deltaTime);
         }
         
         if (up == false)    
         {
         controller.Move(Vector3.down * speed * Time.deltaTime);
         }
         
     if (Time.time > onTime) {
     
         startOn = false;
         yield WaitForSeconds (pause);
         onTime = Time.time + onTime;
         startOn = true;
         }
 
 }
 
 function Update () {
 
 if (startOn == true)
 Movement();
 
 }