Both Laptop screen and Monitor screen show the display but when disconnected from external monitor laptop screen becomes black.
Try to reboot from laptop disconnected to external monitor. It boots with windows welcome sound but the screen is black with no function keys don't work at all.
When plugged in to ext. Monitor it shows the displays on the both laptop and monitor.
Updated the graphic driver to 2016(Latest) still the same issue (Can only install lenovo manufacture drivers)
Uninstalled the graphic driver went back to Microsoft Generic Display and that works with no problem but can't project to an another monitor or projector
Added (1). Upgraded the graphic driver to 2019 still the same issue.