After I managed to fix problems with wireless and graphics, I ran into a problem with KDE(nothing too serious).

I have a laptop and often it is plugged into an external monitor via HDMI. This works without problems.

Installed system is Debian jessie

The problem is following. I go to display configuration and I turn off the laptop monitor. It should switch to an external monitor and it does for about 3 secs and than it turns on the laptop monitor back on and reports

Executable: kded4 Segmentation fault

Can anyone shed any light on the matter.

Did you try to manage your monitors manually in the "Size & Orientation" section, instead of doing that in "Display Configuration"? The first offers in fact some more control. You might try to enable both monitors with their native resolutions, then define the external monitor's position as a "Clone" of the primary one. Check if both are showing your desktop properly. If the external monitor's resolution is smaller than the primary one's (i.e. it doesn't cover the whole desktop), then assign the smaller resolution to both. Finally, try to disable the default monitor in its "Size" field.

Ok so a stupid solution to a stupid problem. Just set whichever monitor you wish to remain running to be the primary monitor and turn the other one off.

Not sure about the tone of your comment. Next time if you don't want a "stupid solution", which apparently solved your "stupid problem", think twice before opening a thread and wasting other people's time.

P.S. You're welcome.