frog rotation/jumping - cant get input keys to work after adding Quaternion code.

private Animator playerAnimator;
private float moveHorizontal;
private float moveVertical;
private Vector3 movement;
private float turningSpeed = 20f;
private Rigidbody playerRigidbody;

    // Use this for initialization
void Start () 
{

    // Gather the components from the Player GameObject.
    playerAnimator = GetComponent<Animator> ();
    playerRigidbody = GetComponent<Rigidbody> ();

}

// Update is called once per frame
void Update () {

    //Gather input from the keyboard
    moveHorizontal = Input.GetAxisRaw ("Horizontal");
    moveVertical = Input.GetAxisRaw ("Vertical");

    movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
}

void FixedUpdate () {

    //if the players movement vector does not equal zero...
    if (movement != Vector3.zero) { 

        // ...then create a target rotation on the movement vector...
        Quaternion targetRotation = Quaternion.LookRotation(movement, Vector3.up);

        //...and create another rotation that fills anim gap between current rotation and target rotation so less jumpy
        Quaternion newRotation = Quaternion.Lerp (playerRigidbody.rotation, targetRotation, turningSpeed * Time.deltaTime);

        //...and change the players rotation to the new incremental rotation
        playerRigidbody.MoveRotation(newRotation);

        // ...then play the jump animation.
        playerAnimator.SetFloat ("Speed", 3f);
    } else {
        // otherwise don't play the jump animation.
        playerAnimator.SetFloat ("Speed", 0f);
    }
}