Having taught some introductory CS courses a few years ago, the amount of struggling with basic things like file naming, directory hierarchies, and even simple hardware use was a constant distraction.
On one memorable occasion, I had to help a student by turning on the monitor: he would sit down at a workstation, move the mouse and tap the keyboard, and seeing nothing show up on the monitor after a moment, go to another unoccupied one. I watched, without intervention, him try this with all the unoccupied workstations in the lab until he finally came to me and said, in an exasperated tone, "all the computers left are broken!" I lead him over to one, and upon pressing the power button on the monitor, the expression he made was quite unforgettable...