NEED URGENT HELP - collision detection

I have a simple game where you jump oncoming barrels. When you are knocked off the platform you hit a collider. The barrels also hit this collider and I want to use it to detect if the players has been knocked off the platform. This is used to show the death screen and give the option to retry the game. The current code im running isnt working.

using System.Collections;
using System.Collections.Generic;
using UnityEngine.SceneManagement;
using UnityEngine;

public class Death : MonoBehaviour
{
public bool Dead;
public GameObject PauseMenuUI;

// Use this for initialization
void Start () 
{
	Dead = false;
	PauseMenuUI.SetActive (false);
}

// Update is called once per frame
void OnCollisionEnter(Collision col)
{	
	if (col.gameObject.name == "Player");
	{
		Dead = true;
	}
}

void Update ()
{
	if (Dead == true);
	{
		PauseMenuUI.SetActive(true);
	}
}

}

@singularcard Your code is fine. Although you should activate the pause menu directly from OnCollisionEnter() and not Update() for optimisation. The problem might be with components you use to detect collision or physics settings (unlikely). I recommend using triggers. Make the collider the player touches when fallen a trigger and then use OnTriggerEnter(Collider col) to detect it. Also this script should be attached to to the trigger collider.