On most laptops, there is a keyboard shortcut to change your display; if you tell me what model laptop you have, I can tell you what that keyboard shortcut is for sure, but on most it is Fn-F8. You should have a function key on the lower left of your keyboard, press and hold this key, then hit the F8 key; this should work at any point after you turn on the laptop. You may need to do it 2-3 times to cycle through the various options, but give it a few seconds in between each press to make sure the monitor has time to turn on.