Many fixes will be easy to identify: make controls more visible, add or change labels, move controls, provide better feedback, etc.
Difficult problems are when the user may not realize that the next
action from the list of correct actions is the one that should be
performed next.
In the example walkthrough
the user may not realize the PC is not turned on, because she
thinks a computer is always on.
In the example, users could be easily trained to recognize the dark screen
as a power-off condition of the PC or the screen by making sure that
every screen saver still displays something on the screen.