I recently updated Kubuntu 15.10 to 16.04... dont know why... never update a fully working system...

Nevertheless I did it and now have a serious problem: When I now start my PC the KDE login screen appears and freezes. Mouse freezed, nothing moves. No keyboard input accepted. The only way now to start my pc is crawling under my PC, disconnecting my displayport monitor(I have 2 monitors, the second is HDMI), restart, wait for KDE Login Screen and reconnect my display port monitor. In this case everything works well. As this is no option I'll have to downgrade to an older version of Kubuntu to remove this new "freezing" feature.

Is there any way to resolve this issue, or, to find out what causes this problem?

Thanks for your help!



(I've already run apt-get update / apt-get upgrade in hope this is a known and resolved issue. Bad luck.)