Rotation along the x-axis to that player can turn around?

Ok I am working on a 3D project where my player piece is navigating through a maze. I can't make it rotate on the X axis. It can move left and right but it does not turn. So the view is only straight forward. My Code is below. You can see in my comments i am trying everything. Please Help!

 #pragma strict
 
 var speed : float = 2;
 var distToGround: float;
 var centerOfMass : Transform;
 var cam : Transform;
 
 
 function Start()
 {
   // get the distance to ground
   distToGround = collider.bounds.extents.y;
 }
  
  
  
 function IsGrounded(): boolean 
 {
   return Physics.Raycast(transform.position, -Vector3.up, distToGround + 0.1);
 }
 
 
 
 function FixedUpdate () 
 
 {
 //THe directions the player peice will go based the keyboard arrows
     var moveHorizontal : float=  Input.GetAxis ("Horizontal");
     var moveVertical : float= Input.GetAxis ("Vertical");
     
     var movement : Vector3 = new Vector3 (moveHorizontal,0.0f,moveVertical); 
 
 
 // When the player peice turns left or right, it tilts slightly
     rigidbody.rotation = Quaternion.Euler (0.0f, rigidbody.velocity.x, 0.0f);
    
    
 // The acceleration for the player peice 
     var XYVelocity = rigidbody.velocity;
     rigidbody.velocity = movement * speed;
 
 
 // The Camera is following the player peice
     rigidbody.AddForce (transform.rotation * cam.transform.forward * moveVertical);
     rigidbody.AddForce (transform.rotation * cam.transform.right * moveHorizontal);
 }