Kubuntu: Laptop screen locked in HDMI-cable-connected-modus

Problem

During boot the KDE startup screen seems to lock on the laptop. Only when I plug in the HDMI cable, the laptop screen starts functioning again. But when I unplug the HDMI cable, the laptop screen turns black.

Environment

• Kubuntu-14.04
• Laptop Lenovo Thinkpad S540

Solution

Somehow the laptop screen failed to restore itself after disconnecting the HDMI cable. Solution was to lookup the laptop screen name via:

xrandr

In my case this was 'eDP1'. Then I typed in a console:

xrandr --output eDP1 --auto

and pressed Enter after having unplugged the HDMI cable, so with a black laptop screen.