There I was, happily working away, screen in portrait orientation, screen resolution set left... seeking some soothing music, opened Amarok (for first time - let it search for music) set Amarok playing, then absent mindedly clicked on an MP3 recording, Movie player tried to open it, Then all mayhem let loose, screen went blank, Both players continued to produce sound but the computer was unreachable. Finally in desperation I held the power button down to force shutdown.
System now rebooted BUT trying to change anything (resolution or screen orientation with "Screen resolution preferences" has no effect. Niether does "xrandr -o-left" in a terminal.
Does anyone know what may have broken?