"and had managed to turn the rotary contrast knob right down"
yup , ive seen that .
plus many other idiotic reasons for screaming THE SYSTEM IS DOWN!!
the screen is off
the app is minimised
someone has opened ebay.com on top of it
someone has changed to a different screen in the app and user dosent recognise
user cant navigate to a particular part of the system.
and this is , of course , always the users opinion of their client PC not "the system"