SpinFlight,
Thank you, you have just reminded me of a similar set of incidents.
Eldest son was working p/t at Maplin a few years ago and bought (well Dad bought it for him) a Mobo/AMD CPU/Cooler combo. Found it needed an uprated PSU so bought a new case and it was left to me to put it all together.
Popped AMD CPU into mobo and applied thermal cream, then promptly ignored the step on the side of the heatsink which should have keyed against the CPU carrier and so ended up putting the heatsink on the wrong way around. I must add in mitigation here that in preparing for this I had read on a web site that the AMD heatsinks were hard to get on, so thought my struggles were the norm.
Of course we turned the PC on and after about 5 seconds everything went blank and the fan wouldn't spin.
Son's pals at Maplin kindly explained that the heatsink being wrong way around had left enought of a gap that the CPU fried, so I had to buy another at full price.
Funnily enough, never had that problem on PCs built since
Spinflight - you reminded me that a couple of years later the PC itself fell over while running & everything went off. I suspected the mobo so bought a new one, then swapped the CPU, and only then bought a new PSU. It was the PSU that was at fault & everything else still worked a treat.