Linux system is weird

Hello, 
I know the following will be somewhat unspecific, but maybe someone has a simple explanation based on my attempt. "Did you try to switch it offandonagain?" Yes already. The machine also seems to move normal, but the Linux desktop cannot be operated normal. 

I left the machine on and coming to the workshop today I could not see the Axis window anymore. 
The complete desktop behaves strange. 

After re-start and unplugging the screen I could start Axis Gui. I cannot move the axis window or re-size it. 
Something is odd it seems. 
Either something is really damaged on the installation or I have accidently changed some setting that I am not aware of. 

Also usually there was a bunch of software things visible and that seems to be missing. 

 

 
The menue bar in the upper screen is missing and the blue menue of the Axis GUI is missing. And I do not know why. 

The next screen shot is from the other machine and that is what the first machine looked like a few days back. 
 
 

I was clicking more or less randomly. Found an option (which I cannot find again) to choose in a session manager what saved session to start during login.

I deleted that session and now it works again.

I still would be interested to learn what I might have done wrong in the first place.