Enemy Select

Im having a real tough time programming this script basically what im trying to do is program my game so that i can select enemies with my mouse but all it does when i click the mouse is cycle through my enemies no matter where i click, i posted this many times and all ive can up with was dead ends i am very new to unity and programming so if you can alter or re write this script in c# it would be greatly appreciated thanks

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 public class Targeting : MonoBehaviour {
  public List<Transform> targets;
  public Transform selectedTarget;
  
  private Transform myTransform;
  
   // Use this for initialization
  void Start () {
   targets = new List<Transform>();
   selectedTarget = null;
   myTransform = transform;
   
   AddAllEnemies();
  }
  
  public void AddAllEnemies()
  {
   GameObject[] go = GameObject.FindGameObjectsWithTag("Enemy");
   
   foreach(GameObject enemy in go)
    AddTarget(enemy.transform);
  }
  
  public void AddTarget(Transform enemy)
  {
   targets.Add(enemy);
  }
  
  private void SortTargetsByDistance()
  {
   targets.Sort(delegate(Transform t1, Transform t2) {
           return Vector3.Distance(t1.position, myTransform.position).CompareTo(Vector3.Distance(t2.position, myTransform.position));
              });
  }
   private void TargetEnemy()
  {
   if(selectedTarget == null)
   {
    SortTargetsByDistance();
   selectedTarget = targets[0];
   }
   else
   {
   int index = targets.IndexOf(selectedTarget);
   
    if(index < targets.Count - 1)
    {
     index++;
    }
    else
    {
     index = 0;
    }
    DeselectTarget();
    selectedTarget = targets[index];
   }
    SelectTarget();
   }
   
   private void SelectTarget()
  {
   selectedTarget.renderer.material.color = Color.red;
   
   PlayerAttack pa = (PlayerAttack)GetComponent("PlayerAttack");
   
   pa.target = selectedTarget.gameObject;
  }
  
  private void DeselectTarget()
  {
   selectedTarget.renderer.material.color = Color.blue;
   selectedTarget = null;
  }
  
   // Update is called once per frame
  void Update(){
   
   //Only search if clicked
     if( Input.GetMouseButtonDown(0) ){
             
             TargetEnemy();
         }
     }
 }