I am using Kubuntu 15.04 on my PC. The system worked fine until it broke a few days ago.
I was creating some data file backup copying files from one data disk to another data disk (the linux system disk was not involved) using luckybackup/rsync. The files were copied correctly but it took some time so I decided to start a game using Wine/PlayOnLinux. However the game (that used to work before) did not open up. Instead two of my three screens turned black. Only the backup output window stayed visible. I stopped the backup procedure and tried to shut down the system. That failed. So I forced a shutdown and booted the system.
Now after entering the password at login screen the cursor turns to a cross and all screens turn black. I can not do anything. Even starting some console by + does not work anymore (the mouse cursor hides but I can not see a prompt).
I tried to login using a different account... same problem.
The system had rebooted fine a few minutes before. I did not install new software or updates in between.
There is a lot of information in the Web about black screens after login but most of these cases are outdated and/or user account related while my problem is account independant. Anyway I tried some of those tips (starting Kubuntu in safe mode) but none worked.
So I (desperately) need beginners level help to fix the problem (without loosing all my settings and installed software if possible).