I sold an AMD XP2400+ system to a female friend, the system worked 110%, NP at my place under any test known.
She took it home and the main board died the next day, I replaced it, OK Not likely I would get another call but again the following day after full rebuild she tells me it has no display and that the CDROM failed, OK I fix it at my cost because she was a good friend but I was getting a bit annoyed, just a bit.
Bla Bla etc similar things continue to go wrong (at her house) only during the next week.
I put in another motherboard and then I said enough, I took it home and all ran it all day and night, it worked again 110% again after a new rebuild, and so it should, the system could not be faulted, OK so she gets it delivered and you guessed right she called again "the PC don't work again and I asked her to come to my shop ans show me what she was doing to see just what she could possibly be doing to them.
By this time I had enough and wanted to test the wiring in her unit on a complete and total hunch, BINGO the extension lead she was using had a complete circuit from both + and - to the third wire, the earth, problem found, and I cut the lead into pieces, from then on it worked fine.
That lesson cost me three BRAND NEW boards and several other NEW internal parts, power supply, Vid cards, CDROMS, floppys etc, etc, etc, for a lousy stinking $5 extension lead.
Evil spirits among others was on the list of possible faults, hardware just don't die like that, Yes it can, I watched it die.
[bleep] happens, call a priest for an exorcisim ? so when you think all possible faults have been looked at, the real fault could be so very small and simple.
That XP box cost me more than I want to ever remember, I now check all power boards and leads no matter what.