I've done that by mistake on a laptop where I set it to use the external only.
Try a few things.
1. Boot into SAFE MODE. What happens?
2. Windows reset may not override that display setting. For your model which Function key sets your display? I can't tell you this as the make and model is missing.
3. It is possible that the laptop has failed. As a test I boot up one of my Linux USB sticks. Try that. Boot any current OS that is on some USB stick. You don't have to know that other OS. It's a test to see if it's some hardware issue.
Hi, so recently I have had some problems with my laptop display not working. I have a Lenovo Yoga 900 and when I went to turn it on last, the screen randomly was black when I started it up. So, knowing a few things about computer problem solving, I messed around in the bios and messed up a few things but was able to fix them, but still had the black screen. And the unusual thing is that the screen works in the bios menu and will display the lenovo logo when starting up as well as the loading symbol but as soon as I would normally come to the login page, the screen goes blank. So, I connected an external monitor which lit up fine and worked great. Also another unusual thing is when I go into settings with the external monitor plugged in, and when I switch the display mode from second screen only to first screen only or duplicate these displays, the screen stays black and the settings immediately switch back to second display only. Also, in the display settings, it says that the first display isn't active. But anyways, I also opened the laptop up, and unplugged the battery, hard drive, and screen and replugged them all back in and the screen still stayed black. So I went further and (on the external display) and made sure that in device manager and configuration settings, that everything was enabled that should be. And after that had no result, I reset windows hoping it would fix the problem, which it did not do. So, currently I am at a loss on what to do as I have done everything I could find as a possible fix and would greatly appreciate any help, suggestions, or criticism on things to do as I would love to get my laptop screen working again.