Is it plugged in?
One of my favorites from the days of a sales department with dial up modems went more or less like this:-
Day 1
Caller "Hi this new computer you gave me can't call the servers. This modem doesnt work"
Me "Hi, is it plugged in?"
Caller "Yes - of course."
Me "Did you follow the guide?"
Caller "Yes, in every detail."
Me "Ok - we often get a problem with broken cables, let us send you a new one."
... snip for a few weeks of couriers, replacement parts and irritation ...
Day 15
Caller "Still doesn't work. I want more help."
Me "Lets go through it one more time. Is it all setup?
Caller "Yes"
Me "Its plugged in?"
Caller "Yes"
Me "Ok start it up. Whats that noise?"
Caller "Well once I can hear the modem dialling I have to plug it into the wall".
Me "Aaaaagh"