Hi there, I have been a happy user of KDE Neon, 5.9.4, 64bit user edition, on a Delll Precision Laptop for roughly 1 1/2 months. Dualbooting with Windows 10 as I can't move everything over to Linux yet.
Today, after a reboot, I am stuck on the Neon/KDE logon screen. The system boots up without problems, asks for my credentials and after I hit enter shows a black screen with a blinking coursor for a second or 2 and then returns to the KDE logon screen.
Sometimes I think I can spot a text based logon message before it switches back, but things happen too quickick to really tell.
An endless loop I don't know how to break out. It doesn't seem to be a password related issue as when I type in same garbage the system tells me that an invalid password was entered.
So what changed? Well, today for the first time, I had the system plugged into my docking station with two screens attached. I also added a simple script copying a file from one place to another to autorun (via the GUI) to run before KDE starts.

Out of the many reboot attempts I today, one didn't take me into the graphical logon screens but presented the main console. I was able to logon but not able to start KDE, startkde came back with something like $DISPLAY not defined.
startx didn't work either. A quick switch to an all black screen and then back into the console. Unfortunately I am not able to reproduce this one.

Any help would be really aprechiated. Don't want to go down the typical "Windows style" reinstall everything route...

Thomas

By the way, this is my first post here, I hope I picked the right workspace?

Edit:
Managed to logon as root in a terminal session again. When I run startX it even starts up KDE, albeit a very limited environment without network, etc.
I then did a su - "myusername" and tried startx again and it won't start.
To me this looks like my useraccount somehow still got the dual screen setup configured and hence will fail to load the KDEl UI.
While browsing the internet for help I stumbled over Xrandr, which is supposed to show the screen settings. In my case it comes back with "can't open display"
Is there any way to reset the X-server, or a file I need change,...?

This may be fairly simple for someone who knows how X11 works, but I am lost I am afraid...

Edit2: After hours of sifting through log files I found the error. I added a shell script to download an updated wallpaper before KDE starts which produced an error. That simple fact made the logon impossible.
Lots of entries like these in .xsessions-errors:
OpenGL version: 3.
Loading stage "initial" 46
/usr/bin/x-session-manager: 38: /home/thomas/.config/plasma-workspace/env/bing-wallpaper.sh: [[: not found
/usr/bin/x-session-manager: 84: /home/thomas/.config/plasma-workspace/env/bing-wallpaper.sh: Syntax error: "(" unexpected
Xsession: X session started for thomas at Do 13. Apr 16:57:32 CEST 2017
localuser:thomas being added to access control list

Renaming the script in .config/plasma-workspace/env solved things immediately. Shouldn't such a simple error be caught by the platform? Anyway, I got my Neon back!
Maybe this helps someone else...
Thomas