It depends on your laptop what key combination you have to do. For example this picture.http://www.accessoriesrepair.org/wp-content/uploads/2012/06/laptop_keyboard.jpg
You will have to press FN+F7 for the picture mentioned above. You see on F7 the screen with the arrow.
A keyboard like this one http://www.p-wholesale.com/upimg/18/65a1/laptop-keyboard-for-hp-x1000-954.jpg
You will have to press FN+F4
Press the keybuttons and see if it works for you. Sometimes you have to do it 2 times to get it to work.