贪食蛇！

贪食蛇求助！！！
现在场地和蛇都已经做好了，蛇也能动，就是键盘怎么按都没用，下面是代码，求大神解答~~~~~~~
       private void Start_KeyDown(object sender,KeyEventArgs e)
        {
            int pressKeyValue;
            int direction = myFloor.CurrentSnake.Direction;
            pressKeyValue = e.KeyValue;
            if (pressKeyValue == 37)
                direction = 3;
            else if (pressKeyValue == 38)
                direction = 0;
            else if (pressKeyValue == 39)
                direction = 1;
            else if (pressKeyValue == 40)
                direction = 2;
            myFloor.CurrentSnake.TurnDirection(direction);
        }