Kill player when hit Groung (JavaScript)

Well, i'm making an FPS the map is like a roof, so when you fall and hit the ground, you die, i tried lot's of methods i found here in Unity Answers but none of them worked, so, basicly, when I hit the Terrain(Untagget), the Player Cameras (FPS and Minimap) are disabled, and the DeathCamera is enabled. Well, but this is not my problem, my problem is that, if I use OnTriggerEnter, everything that hits the ground dies, and if I use OnCollisionEnter (them search by tag "Player") nothing happens when i hit the ground.

here's my code, if somebody can help me, thanks a lot, and sorry for my english, i'm from Brazil.

[JAVASCRIPT] Fall.js

 #pragma strict
 
 var fpsCamera : Camera;
 var minimapCamera : Camera;
 var gameoverCamera : Camera;
 var skinDead : GUISkin;
 var isDead : boolean = false;
 
 function Start(){
     fpsCamera.enabled = true;
     minimapCamera.enabled = true;
     gameoverCamera.enabled = false;  
 }    
 function OnCollisionEnter(collision : Collision){
     if(collision.gameObject.tag == "Player"){
         isDead = true;
         DieFunc();
     }
 } 
 function DieFunc(){
     fpsCamera.enabled = false;
     minimapCamera.enabled = false;
     gameoverCamera.enabled = true;
     yield WaitForSeconds (5);
     Application.LoadLevel("#1"); 
 }  
 function OnGUI(){
     GUI.skin = skinDead;
         if(isDead){
             GUI.Label(Rect(Screen.width /2 -60,Screen.height /2,500,500), "You're Dead");
         }
     }

(All variables are assigned, removed empty spaces to make the text smaller)

Thanks!