The laptop screen was working fine until I connected an external monitor. I had the display setting on "extended" mode. I shut down the computer when i was done working and when I turned it back on the laptop display was completely black, but the external monitor worked fine. I tried going into the monitor settings but nothing would work.
Your laptop has a "F" key with a laptop & desktop icon. Press the "Fn" key & the "F" key with the monitor display and you should be able to switch displays between either your laptop, desktop, or both.
I have a Dell and for me, it's Fn + F8