Health script

Hi guys, I'm having an issue with my health script. I've been following the BurgZerg tuts on nGUI vital bars and I have everything working except for the parts I want to add. For example and "game over" state and reducing scores (playerPrefs) when you are dead. Any suggestions?

 using UnityEngine;
 using System.Collections;
 
 public class VitalBarBasic : MonoBehaviour {
     
     public UISlider _slider;
     public float _maxWidth;
     
     
     void Awake()
     {
         _slider = GetComponent<UISlider>();
         
         if (_slider == null)
         {
             Debug.LogError("Could not find UISlider");
             return;
         }
         
         _maxWidth = _slider.foreground.localScale.x;
     }
     
 
     // Use this for initialization
     void Start () {        
         UpdateDisplay(1);
     }
     
     void Update()
     {
         
     }
     
     // Update is called once per frame
     public void UpdateDisplay ( float x ) {        
         
         if(    x < 0)
         {
             Debug.Log ("Game Over");
             PlayerPrefs.SetInt("High Score", PlayerPrefs.GetInt("High Score") - 25);
             x = 0;
         }
                 
     else if( x > 1 )
 
             x = 1;
     }
     
     public void DamageTaken ( float x ) {    
 
         _slider.sliderValue -= x;
         
         if(    x < 0)
         
             PlayerPrefs.SetInt("High Score", PlayerPrefs.GetInt("High Score") - 25);
     }
     
     
 }