How to store a gameobject in a variable

I have a script attached to a cube in my project, I want to activate and deactivate the cube when I press return and shift key respectively, but I can’t do that in the script attached to the object as once the object is disabled, the script can’t be accessed anymore, so I created another cube and attached a script to it, I put in this code:

using UnityEngine;
using System.Collections;

public class Enable_Disable_Script : MonoBehaviour {
	private cubeScript myScript; 

	// Use this for initialization
	void Start () 
	{
		myScript = new cubeScript();
	}
	
	// Update is called once per frame
	void Update () 
	{
		if (Input.GetKeyDown (KeyCode.Return)) {
			myScript.Cube.SetActive (false);
		} 
		else if (Input.GetKeyUp (KeyCode.Return)) 
		{
			myScript.Cube.SetActive(true);
		}
	}
}

NOTE: ‘cubeScript’ is the script I attached to the first cube and ‘Cube’ is the name of the variable I want to store my cube gameobject in.

My question is - How can I store the cube(gameobject) that I want to activate/deactivate in the variable ‘Cube’ by using some code in the first script?

Please help, I am a beginner in unity and I don’t know how to do this, I have tried each and everything I knew and nothing is working, I have spent hours trying to figure it out, but it seems I am getting it wrong somehow, any help will be appreciated!

I think you should make a game object and put this script on it:

public GameObject Cube; // You’ll have to put your cube into the slot in the inspector.

void Update()
{

     if (Input.GetKeyDown (KeyCode.Return)) {
         Cube.SetActive(false);
     } 
     else if (Input.GetKeyUp (KeyCode.Return)) 
     {
         Cube.SetActive(true);
     }

}