I have a Sony Vaio.
The problem started after I was resetting windows 10 , i'v left my computer on for nearly about 6~7 hours for the reset cuz nothing was showing up on my external monitor. When I came to check on it everything was working fan, number lock light caps, on the laptop works expect the external monitor. I repeatedly tried Fn + f11 and also Fn+f4 and alt number lock but there still respond.
iv also tried removing the montior screen and connect external monitor and still no luck.