GameObject won't move after got child

Sorry for the basic question, I am quite new in unity. So I use the FPS Controller from Unity. That is also my parent game object. I have another game object which is a book with the script down below..

So the problem is that after I set the parent of the book. I cant move.... I don't get an error or something.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityStandardAssets.Characters.FirstPerson;
 using UnityEngine.UI;
 public class bookCollider : MonoBehaviour {
 
     FirstPersonController playerController=null;
     public Text clicktext;
     private bool isInTrigger=false;
 
     GameObject gameControllerObject;
 
     void Start(){
          gameControllerObject = GameObject.FindGameObjectWithTag ("FirstPersonController");
 
         if (gameControllerObject != null)
         {
             playerController = gameControllerObject.GetComponent <FirstPersonController>(); //here is the error
         }
         if (playerController == null)
         {
             Debug.Log ("Cannot find 'FirstPersonController' script");
         }
     }
 
     void Update(){
         if (isInTrigger) {
             if (Input.GetKeyDown (KeyCode.F)) {
                 gameObject.SetActive (false);
                 clicktext.text = "u picked that item up";
                 Invoke ("setTextToDefault", 2f);
 
             }
             if (Input.GetKeyDown (KeyCode.I)) {
                 this.transform.parent = gameControllerObject.transform; //after here I cant move backwars/forward/sideways
                 clicktext.text = "added to int";
                 Invoke ("setTextToDefault", 2f);
 
             }
         }
 
     }
 
     private void setTextToDefault(){
         clicktext.text = "";
     }
     void OnTriggerEnter(Collider other) {
     //    Destroy(gameObject);
     //    playerController.PlayJumpSound ();
         clicktext.text=" f:pick up item.I:add to inventar";
         isInTrigger = true;
         Debug.Log ("jojojo");
     }
 
     void OnTriggerExit(Collider other) {
         clicktext.text="";
         isInTrigger = false;
         Debug.Log ("lol mate u out");
     }
 }