Hi, my laptop display is not working correctly. I have windows 10 64-bit installed and when I boot up, I see the windows logo and loading screen then the display just goes black. Works completely fine when using an external monitor as an only screen. I don't think it's a hardware issue because when I press ctrl+shift+windows+b then the screen flashes a near perfect image. Also I noticed when watching youtube videos in full screen that if most of the output frame is black, the laptop display will show that mostly black frame.
Sounds like a driver issue. The BIOS displays the startup logo and then when Windows is loaded, a graphics driver is used. Use the Lenovo help utility to check if there are driver updates available. If that doesn't work, try to remove and reinstall the driver. Another way to confirm the issue is startup in safe mode with VGA driver chosen.