I plugged the HDMI connector and turned on the computer, but when the log in screen appears the laptop screen appears split in 2, one top and one bottom. The external monitor connected via HDMI works fine. I just need to know how do I disable dual screen from laptop and back to normal.
I found this answer. Does this help you? It says:
I plugged the HDMI cable in (caused screen split) then took it out and closed the lid. When I opened the laptop and logged back in it allowed me to connect the second monitor.