Note that this will reset some stuff like the favorites in the startmenu.
Browse to ~/.local/share/kactivitymanagerd/resources/ and delete the files there but keep the backup folders. Afterwards logout and back in or reboot.
See Monit.
There's a problem being unable to change resolution from 1152x864 to anything else. The workaround is to disable the KScreen 2 background service in System Settings - Startup and Shutdown - Background Services.