External Monitor question

Hello, my laptop screen cracked, and I had it hooked up to a monitor that I use for multiple purposes. I don't know why, but I decided to let my brother use the laptop, and he started messing with screen options, where it shows like screen 1 screen 2, and the resolution. Well I have no idea what happened, but now, when I use the laptop I get the windows xp start up, and the acer load out screen, and then my monitor goes black, and my broken screen lights up. I've tried the fn-F5 button stuff, doesn't work, just hoping there's another way to change it, so I can see it on my monitor, as I can't do anything with a broken laptop screen, I would try to fix it, but money is tight, and most of my. Things are on the laptop. Thanks help would be greatly appreciated.