[Solved]cant disable/enable scripts

private CameraFollow follow;
private CameraFollow follow;
private MouseLook look;

	// Use this for initialization
	void Start () {
		transform.parent = null;
		look = Camera.main.GetComponent<MouseLook>();
		follow = Camera.main.GetComponent<CameraFollow>();
	}
	
	// Update is called once per frame
	void Update () 
	{
		GameObject target = GameObject.Find("pc");
		if(Input.GetAxis("Mouse ScrollWheel") > 0)
		{
			transform.parent = target.transform;
			look.enabled = false;
			follow.enabled = true;
		}
		if(Input.GetAxis("Mouse ScrollWheel") < 0)
		{
			transform.parent = null;
			look.enabled = true;
			follow.enabled = false;
		}
	}

I try to disable my third person camera on zoom in and disable my first person camera on zoom out but this script tends to error nullreference object I fail to see what is my error

The first thing I notice is that you have the top two lines repeating themselves, I doubt this would compile so it must be a copy/paste error?

The next thing I notice is that these three lines could result in null references:

look = Camera.main.GetComponent<MouseLook>();
follow = Camera.main.GetComponent<CameraFollow>();
GameObject target = GameObject.Find("pc");

It is good practice to perform null checking (at least when debugging) after operations like these.

It can be as simple as:

look = Camera.main.GetComponent<MouseLook>();
if(look == null) {
    Debug.Log("GetComponent<MouseLook>() returned null");
}

If you perform a similar check after each line identified above you should be able to determine when the nulls are creeping in.