I had a customer come in with his computer (an eMachine) and it didn't work, I open the case only to find the SouthBridge had melted...I have no ideea how that happened.
My old CRT monitor's flyback fractured causing a loud sparking noise and the most god awful smell I ever smelled.
Got a shipment of PCs all banged up, luckily, only the case was damaged and nothing else (some shipping companies are the worst).
We had a thunderstorm a while back and after one very close lightning strike, my PC shut down. I couldn't start it and thought that lightning had hit it...luckily, I switched the PSU's switch Off and back On and it booted right up.
Had a person come to the store with an Athlon XP that had all its pins bent, he tried to put it into his Socket 370 mobo...after I went away to laugh it off, I slowly bent all the pins back as straight as possible and put it into a Socket A mobo and saw it was working; I came back to the guy and told him that he was lucky and to never try putting an AMD chip in an Intel mobo again or I will not unbend the pins back...the guy paid turned around in shame and never returned to the store again.
Oh, and mobos with bad caps, I got a nice (big) collection, mostly are VIa mobos, but I've got some Epox and Abit mobos in there also.
I got this other customer that came into the store and he said his computer was acting weird, so I took a look inside and bad caps all around...luckily, I had in hand some mobos from a company that used good caps and had the exact same chipset and peripherals, so I dismantled his PC, built it up and to my unpleasant surprise, his HD died on me (those damn 60GB HDs, you can put a functional 60GB HD on a counter for a month then put it into a PC and its dead).