College Computer Switch Problem

A long time ago, I worked as a helper in a college computer facility. On the first day of a class, the instructor told the students to turn on their machines. He dutifully explained that not only do you have to flip the big switch located at the rear right (these were old XT and AT machines) but also to turn the switch on the monitor. One intelligent-looking fellow followed the instructions to the letter. He flipped both switches but did not see the screen light up. He tried both switches again but still no luck. He tried this for minutes to no avail. You're probably guessing the plug was out, or the contrast knob was turned all the way down. Nope. The computer was already on when he got there, but the monitor was off. He never managed to get both turned on at the same time.