Back when I was in highschool I was disassembling my old pc (perhaps gutting for parts can't remember) in anticipation of a new upgraded one that I was about to get. On the back of the power supply there was this little red switch which I was always curious about. Thinking that I had unplugged my pc (I had not) I flipped the switch....
BANG!
Queue a gaping hole in the side casing of the power supply. I remember thinking that it looked like I bullet had gone through it :P

Then there was the one time a friend was building a pc for me and forgot / didn't know he had to put thermal paste between the cpu and the heat sink. The cpu fried pretty much immediately :P

Anyone other stories like that?

Depends... Nothing quite as dramatic as that. I'm fairly sure I killed my last laptop through overheating by playing games on it.. it used to black out / BSOD a lot and was very hot and eventually the motherboard died, fairly sure the overheating played a part.
Damn you Civ V!

I broke an old Dell laptop because the charging port came away from the motherboard through lack of care with the plug / wire and had to replace the motherboard (at great expense) to fix it.

I'm pretty sure my laptop picked up some overheating damage somewhere along the way as well. If I had to guess I'd say it was over one December a few years back when I played the, up to that point, most taxing game yet on it : STALKER : Clear Sky. I think it was at about that time that I started noticing problems. Next time I spend a lot on a laptop, if ever, I'm going to get one of those cooling platform things with the huge fan to put the laptop on :P

I used inferior thermal paste on my desktop processor. Took about 2 hours to smoke it. I was a sad panda.

Nothing quite that bad. The worst was probably the time I fried my old 386DX/25 by soldering in an 80MHz crystal oscillator. I originally just wanted to bump it to 33MHz but for whatever reason I was unable to obtain a 66MHz oscillator so I dared to chance the higher clocked part. It ran for a brief time at the new 40MHz speed, but rapidly started producing errors and hanging the system. It wasn't a major loss as I had a 486DX/33 also, but it was the machine that ran my BBS. I ended up putting together a 486DX2/66 primary system and relegating the 486DX/33 to running the BBS.

Another time was when a full height SCSI drive which generated significant heat combined with very limited internal space toasted my DEC Alpha Multia system. That one was a freebie though, so no real loss there.

See those files in the "Program files" directory? Turns out you can't move them... I placed them all inside another folder because I didn't like how they were organized and my Windows '95 PC didn't turn back on... Had to reinstall everything.

Yeah, I can highly recommend that. My one isn't even particularly fabulous but I never had an issue with the old laptop after I got one (but I believe it was too late and the damage was already done) and I've never had any trouble with my new one and I always plug the fan in when gaming.

Same here. I always turn it on when I turn my laptop on. This is like my four or fifth laptop in the past 6 or so years and I believe it is because I game on them and they run hot. This one (knock on wood) I've used the laptop cooler on since almost day 1 so I'm hoping this one lasts. So far no problems are showing up (like the BSOD's and lock ups I would see on the others before they finally quit).

As to OP, I was playing a racing game on a Dell desktop I had years ago, very real, like racing game, (NASCAR) in that it takes the same amount of time to run a race in the game as it does IRL (if you run the same distance). I was running the Daytona 500, about maybe 2 hours into the race and got so sleepy I had to go to sleep. Couldn't save the game in a race so I just paused it... and went to sleep.

Woke up to a fried graphics card. LOL. Totally. Fried. Good news was i was able to replace it that day when I got lucky at Best Buy but it was an expense after doing something totally stoopid. LOL

My dad destroyed his by putting Norton on it.

And 30 years ago I once through my Apple// through a window, though it actually didn't damage the computer, just the window. :P

Luckly, I've never damaged anything. O_o'
PC components are damn expensive.. I'd feel very bad.

!. I got RIVA TNT from a friend of mine. I plug it, the card worked excellent outperforming my old card. Then I came with an idea that I should upgrade bios on my card...beep, beep...

2. From a company of mine I bought a nice laptop for my wife. Wanted to get rid of a password on bios. Took me ages to dismantle the thing, removed battery, put it back, password was gone but then I accidentally touched unprotected mainboard's cicruits with a keyboard that had some metal-like layer on the bottom. BZZT..

Oh this one is easy te remember... :-( I think 10 years ago I bought a computer from someone who like to overclock 'm. He had a setup that would freeze (literally) the CPU. There was some sort of tube attached to it that I had to turn on first and then the computer itself.

There was this one time I forgot turn the machine of that freezes the CPU so that thing kept on freezing the CPU, so much that there was some sort of ice build up. The next morning I turned on the freeze thing first (so I actually turned it off), I then turned on the computer and because of the heat the ice melted and short circuited everything inside.

RIP

I have had many an accident with my machines. Here is a sampling, in chronological order:

I can't tell you how many times I returned my C64 to Target after having blown up one of its CIAs. I probably contributed to Commodore's demise thanks to Target's liberal return/replacement policy. Oh, and to add to my shame, the CIAs were blown due to my attaching home-made hardware to the user port, and not a fault of the C64 itself.

I lost my favorite monitor by transporting it in mid-winter and turning it on immediately. Took me years to find a (mostly) better replacement.

I was running out of space on my old hard drive, and got a newer, bigger one. When I issued the command to format it, I typo'd and formatted my running main partition, instead. These days, it would be harder to do that. Took me over a month to recover all the data by examining all the data blocks. Good thing I was out of space, as I had compressed nearly everything on the drive (using an auto-compressing file system), and the compressor kept the old file name, length, and checksum. Also a good thing I had a blank drive to use as an OS and storage for recovered files.

I finally reverse-engineered a vibrating game pad so I could have it vibrating in Linux, as well. As I was putting it together again, I crossed some wires, and it smoked the next time I made it vibrate. As with any such devices, they were no longer sold and all that work was for nothing.

I didn't keep my "machine room" clean enough, which probably resulted in one of my AlphaStation's CPUs' fan clogging and dying. The burned CPU board was spectacular. However, I was able to pull the board and continue running the machine until I got a replacement. By coincidence, the replacement/upgrade machine I bought also had a non-functional second CPU (soldered to the main board, so not possible for me to replace due to lack of solder flow equipment), but this time due to lying, cheating sellers rather than my own fault. Oh well. Alpha is good and dead now, so I guess I don't miss 'em, much.

While wiping my work laptop as I was leaving my last real job, I dropped it and accidentally damaged the optical drive, which was its defining feature (compared to the Mac Air).

I was trying to get a Windows 10 tablet to become a Linux tablet. Sound didn't work. I tried fiddling with the BIOS settings, and ended up bricking it. Bricked it will remain, as I have no intention of letting store "experts" play with the private data I had already transferred to the device. In fact, I have bricked many a cheap tablet due to non-use/battery death, and will probably never buy another.

Walking across a fluffy carpet and plugging in my earbuds into the laptop audio jack. Also using same laptop for video encoding and blowing into the fan exhaust to clean it out while it was under max load. If you do that, it spins faster than it's rated for and starts to smoke.

RIP laptop. You taught me lessons I wouldn't have learned any other way.