hey, Im making a code for a multiple choise question but for some reason when i drag the mouse over it , it does change coler but when i click, it does not, what could be going on?

pragma strict

var correct = true;
var answer = true;
var wrong = false;
var locking = false;

function Start () {
Screen.lockCursor = true;
}

function Update () {
Screen.showCursor = false;
// center mouse   
    if (Input.GetKeyDown(KeyCode.P))
        if (Screen.lockCursor)
        Screen.lockCursor = false;

    else{
    Screen.lockCursor = true;
    }
//if correct
    if (Input.GetButtonDown("fire1")&& answer)
    {
    renderer.material.color = Color.green;
    locking = true;
    }
    if (Input.GetButtonDown("fire1")&& wrong)
    {
    renderer.material.color = Color.red;
    locking = true;
    }
    if (wrong && answer)
    {
    answer = false;
    }

}
// change color when mouse is on
function OnMouseEnter ()
    {
    if (locking = false)
       renderer.material.color = Color.red;
    }

function OnMouseExit ()
    {
    if loking = false; 
       renderer.material.color = Color.white;
    }
thanks a lot