HELP PLEASE!

Im making a game that when the ball hits the floor it will go to the gameover scene.

function OnTriggerEnter(collision : Collision){
if (collision.gameObject.tag == "BOOM"){
Application.LoadLevel ("2");
}

can you tell me whats wrong?

OnTrigger uses collider type, not collision; swap that and try again?

You have to define your TriggerEnter function in following way.

function OnTriggerEnter (other : Collider) {
 if (other .gameObject.compareTag("BOOM")){
    Application.LoadLevel ("2");
 }
}

If you want more information then please read manual.
OnTriggerEnter

Make sure In Inspector window your Collider property isTrigger is true.

 function OnTriggerEnter(collision : Collider){
    if (collision.gameObject.tag == "BOOM"){
    Application.LoadLevel ("2");
    }