How to make my first player controller collidable?

Hi,i made sprint script,IT WORKS PERFECT,but when i walk up to some walls or any objects..... simply i just can walk them through,when i add sprint script,it makes first person controller ignore any collisions or colliders,why?!?!?!? Can someone please fix this?!?!?! PLEASE!?!?!

 var NaturalSpeed = 1;
 var tempSpeed : float;
 var SpeedMultiplier = 3; // for 20% speed increase while sprinting
 
 var moveDirection : Vector3; //this determines which direction we should be moving towards
 
 function Update()
 {
     moveDirection = Vector3.zero; //this rests our move direction to nothing so we wouldn't move unless movement keys were pressed
     tempSpeed = NaturalSpeed; //this rests our speed back to natural speed
 
     //this is just a simple movement check for demonstrating sprint; use your own methods of course
     moveDirection.x += Input.GetAxis("Horizontal");
     moveDirection.z += Input.GetAxis("Vertical");
 
     if(Input.GetKey(KeyCode.LeftShift)) //this checks to see if the player is holding left shift
     {
        tempSpeed *= SpeedMultiplier; //this increases our speed by the multiplier
     }
 
     transform.Translate(moveDirection.normalized * tempSpeed * Time.deltaTime); //this moves our player to the correct direction at the determined speed (sprinted or not), smoothed over time
 }