public bool enabled ;


Enabled Behaviours are Updated, disabled Behaviours are not.

This is shown as the small checkbox in the inspector of the behaviour.

using UnityEngine;
using System.Collections;
using UnityEngine.UI; // Required when Using UI elements.

public class Example : MonoBehaviour { public Image pauseMenu;

public void Start() { //Enables the pause menu UI. pauseMenu.enabled = true; } }