Connecting laptop with broken screen to external monitor

Hello there. So I have been using an external monitor for some time not seeing as my laptop screen is completely shattered. Well my system went to do an update and when it restarted it stopped projecting the screen. (I have a Sony VAIO running windows 7) well I've tried everything I can think of. Even the fn-f7 key (that's my LCD monitor key) and it doesn't work... Thing is I can't tell if I'm pressing it at the right time being I don't know if its bringing me to the screen that says "start windows normally" when I reboot being I cant see the screen at all. I also can't tell if it goes into the login screen or not and nothing I try seems to work. Does anyone know how to fix this? Thanks