I used a video tutorial to make my 2dChar jumping but the Character jumps only 1 time after pressing space. Unity isn’t showing errors 
// Char Speed
var moveSpeed = 4f;
// Jump Player
var jumpHeight : float = 500;
var isJumping : boolean = false;
function Update () {
Movement ();
}
// Movement and Jump
function Movement () {
if(Input.GetKey (KeyCode.D))
{
transform.Translate(Vector2.right * moveSpeed * Time.deltaTime);
}
if (Input.GetKey(KeyCode.A))
{
transform.Translate(-Vector2.right * moveSpeed * Time.deltaTime);
}
if(Input.GetKeyDown(KeyCode.Space))
{
if(isJumping == false){
rigidbody2D.AddForce(Vector2.up * jumpHeight);
isJumping = true;
Debug.Log("isJuming");
}
}
}
// Player is on Ground - for Jump
function OnCollisionEnter2D(col : Collision2D )
{
if(col.gameObject.tag == "Gass")
{
isJumping = false;
Debug.Log("NoJumping!");
}
}
I hope you can help me,
Greetings GreenTee 
jmgek
2
isJumping = true;
Makes it stay true, forever.
float nextTimetoJump;
void Start()
{
nextTimetoJump = 3;
}
void Update()
{
nextTimetoJump -= Time.deltaTime;
if( nextTimetoJump < 0 && Input.GetKeyDown(KeyCode.Space))
{
Movement ();
nextTimetoJump = 3;
}
}
Are you 100% sure that the tag you are using is the right one? i mean the string and tag are exactly the same.