I started in IT as a first-level technician in a university. To bring more pupils in, the university's administration offered a new laptop to every new student, which they could keep if they successfully finished their master's degree.
One day, a student came to the help desk complaining about Windows blue screens of death on his laptop. I used it while he was there and checked for the usual viruses and spywares, did the Windows updates, and gave it back to him.
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About 15 minutes later, he came back with the laptop, saying he just had another BSoD. I said fine, leave the laptop with me for the afternoon; I'd use it to work remotely on my station and see if it would crash again. It didn't. At the end of the day, he came back to pick it up, and everything worked properly.
The next day he came again, complaining about the crashes. I had tried everything I could on the laptop, so I decided to restore the standard OS image and restored his data on top.
He came back; the BSoD kept happening. By then I was convinced it was a hardware issue, so I swapped his hard drive to a new laptop and hoped it would solve all of his problems.
We powered it up together so that he could see if everything was available and working, and he left with his laptop open in his hands. As he walked down the hallway, his computer crashed.
I looked at him, puzzled, and decided to try something. I restarted the laptop and slowly walked down the hallway. At the same spot where he had stood, the computer crashed in my hands.
I thought, "This has something to do with the wireless network."