When a computer starts smoking, it's typically an indication of a problem more severe than one tech support could remedy.
A user phoned me and complained that her monitor was smoking, smelled of burning, the display had gone wrong, and the monitor was too hot to touch. I suggested that she switch the monitor off until an engineer could look at it.
I'm the manager of several computer network and desktop technicians. Recently, a user had been rolled out with a new desktop PC a day earlier. She insisted that this new PC was "giving off some kind of electrical rays or something." When a technician and I got to the user's office, she got a very serious look on her face and brought me over to the offending PC. She placed her hand, palm down on the desk, directly in front of the new computer. "You feel that?" she says. "That's electricity there! I even heard some kind of static on my phone for a second or two, and I've already had the phone guys replace it! FEEL this!"
When I placed my hand on the desk, I felt distinct but almost miniscule vibrations from the PC chassis cooling fan oscillating on the desk surface. Just to check, I had the technician lift the PC about a half-inch off the desk to see if the "electricity" still was present. It wasn't.
Trying hard to suppress the laughter, I told her it was only the cooling fan of the computer and that there was no electricity coursing through her desk. She wasn't happy about it. As we left, she called after us, "Well, if they ever come in here some morning and find me fried, you'll know why!"
Yes. We'll know why.
One of our junior executives called me frantically one afternoon to inform me that his computer was sending out smoke and hissing at him. He said that he had unplugged it but to no avail. I rushed to his office to see. When I got there, I realized that he had over-watered the plants on his window sill and the excess water was running down into the heat register located behind his PC.
A friend of mine ran a 386 without a case. He had all the parts plugged together on his desk, just sitting in the open. One day he was working on it while someone was playing a game on it. What happened was described by him as "blue lightning from the power supply."
He didn't learn his lesson. One day he decided to take apart his monitor. He was in the process of disassembling it when he touched the capacitor. He said his arm felt very strange for several hours. I consider it a miracle that the monitor survived.
We discovered that the poor fellow had inadvertently stepped on his power strip, turning the whole thing off. The monitor make a slight popping noise as it did. And, it turned out, he was smoking a cigar at the time, and he thought the smoke curling around was from the monitor.
By the time we figured that out, though, he'd already emptied a fire extinguisher into the mess.
A few years ago, my daughter took over my computer sales and service business. Although she is probably "techier" than I am now, at the time she was pretty inexperienced, particularly when it came to hardware. As part of her training, she assisted me while I did various repairs. I remember stressing to her, "When diagnosing and repairing problems, it's important to stay calm. If you panic, you'll make mistakes."
We were installing a hard drive in one particular machine. The workbench was cluttered, so she had the case, and I had the keyboard and monitor a few feet away. After plugging everything in, I told her to hit the power switch while I got ready to access the CMOS from the keyboard. I was looking at the monitor when I heard her calmly say, "Ok, now the drive's on fire. Is that normal?"
I had certainly never seen a drive actually burst into flames before (obviously it was VERY faulty), and I immediately shouted in a panicked voice "Turn it off! Turn it off!" My daughter, however, was completely calm.
After a few more repetitions of this, I heard someone, presumably the client's roommate, scream. Then I heard the dorm fire alarm go off in the background. Those things are awful loud, but she didn't seem interested in unplugging the computer, fleeing the fire in her room, or anything else other than arguing with me. Figuring I was doing her a favor, I hung up.
Back when I was in high school, I was in my first programming class. I had downloaded a DOS program. It presents a fake C:\> prompt and prints mildly rude messages instead of executing commands. After showing it to a few classmates, I ran it on the teacher's computer when he wasn't looking. After a few messages, he figured it out. Someone said, "Heh-heh, he did it," and revealed the culprit to be me. Fine.
This particular program, after being rude for about a screen or so, starts getting apologetic, and finally ends with "Wait! Please don't turn me off! Noooooooooooo!" and gives you the real DOS prompt. Right when that message printed, the screen started wavering and dimming. Then smoke began to pour out of the back of the monitor. The screen went completely dead and smoke and big nasty flames were pouring out of the back of the monitor. The teacher had to hit it with the fire extinguisher.
Luckily, he was smart enough to realize that this would be a very hard thing to do in software. It turned out the monitor was so dusty that the power supply had caught on fire. But for a moment I was terrified that I would be held responsible. It was a pretty amazing coincidence of timing.