My frog wont die

private bool gameStarted = false;
[SerializeField]
private Text gameStateText;
[SerializeField]
private GameObject player;
[SerializeField]
private BirdMovement birdMovement;
[SerializeField]
private FollowCamera followCamera;
private float restartDelay = 3f;
private float restartTimer;
private PlayerMovement playerMovement;
private PlayerHealth playerHealth;



// Use this for initialization
void Start () {
    Cursor.visible = false;

    playerMovement = player.GetComponent <PlayerMovement> ();
    playerHealth = player.GetComponent <PlayerHealth> ();

    // Prevent the player from moving at the start of the game
    playerMovement.enabled = false;

    // Prevent the bird from mobing at the start of the game
    birdMovement.enabled = false;

    // Prevent the follow camera from moving from its game position
    followCamera.enabled  = false;

}

// Update is called once per frame
void Update () {
    // If the game is not startet and the player presses the spacebar...
    if (gameStarted == false && Input.GetKeyUp (KeyCode.Space)) {

        // ...then start the game.
        StartGame ();

        // If the player is no longer alive then...
        if (playerHealth.alive == false) {

            //...end the game...
            EndGame ();

            //...increment a timer to count up to restarting...
            restartTimer = restartTimer + Time.deltaTime;

            //... and if it reaches the restart delay...
            if (restartTimer >= restartDelay) {

                // ...then reload the currently loaded scene.
                SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);

            }
        }

    }

}
private void StartGame() {

    // set game state
    gameStarted = true;

    // Removing the start text
    gameStateText.color = Color.clear;

    // Allow the player to move
    playerMovement.enabled = true;

    // Allow the bird to move
    birdMovement.enabled = true;

    // Allow the camera to move
    followCamera.enabled = true;

}

  private void EndGame () {


    // set the game state 
    gameStarted = false;

    // show the game over text
    gameStateText.color = Color.white;
    gameStateText.text = "Game Over!";

    // Remove the player from the game 
    player.SetActive (false);
}
}