I removed Maven2 from my computer and tried installing Maven3. While doing this I added a few things to the /etc/environment file, as instructed by the Maven guys. Anyway, after a few successful log-outs, I logged-out again and suddenly was not be able to log in back, even after booting and shutting down my laptop.
When Ubuntu starts it asks for my password and then I see a blank screen with numbers on the top left and "dwm-5.8.2" on the top right (see images). The only thing I can do is access the command line (ctrl-alt-F2). I did that and modified my /etc/environment file back to the original, but still got the same screen after reboot. When I select the guest user everything starts normally.
I have no idea what's going on. Thanks for your help!