2D platform, jump problem

Hi there, I'm using a rigidbody as player and I'm having problems with the jump function... Sometimes when I press the jump button it simply doesn't work, I believe it have something to do with the jumpEnabled variable, any help is very welcome!

using UnityEngine; using System.Collections;

 public class playerMovement : MonoBehaviour {
     
     public float maxVelocity;
     public float jumpStrenght;
     
     private Vector3 moveVector;
     private bool jumpEnabled;
     
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         if(Input.GetAxis("Horizontal") != 0){
             moveVector = new Vector3(Input.GetAxis("Horizontal")*Time.deltaTime*maxVelocity,rigidbody.velocity.y,rigidbody.velocity.z);
         }else{
             moveVector = new Vector3(0,rigidbody.velocity.y,rigidbody.velocity.z);
         }
         
         rigidbody.velocity = moveVector;
         
         if(Input.GetButtonDown("Jump") && jumpEnabled){
             jump (1);
         }
     }
     
     void OnCollisionEnter(Collision collision){
         if(collision.collider.CompareTag("terrain")){
             jumpEnabled = true;
         }
     }
     void OnCollisionExit(Collision collision){
         if(collision.collider.CompareTag("terrain")){
             jumpEnabled = false;
         }
     }
     
     public void jump(float multiplier){
         rigidbody.AddForce(new Vector3(0,jumpStrenght*multiplier,0));
     }
 }