If something is super fucky and defying all logic, try a different PSU. It's the one thing apart from the motherboard that can effect every area of your PC.
I have a folder of photos on my PC, shared over the network. I could browse that folder fine locally. I could look in other shared folders over the network. If I looked in the photo folder over the network, the PC would power off instantly.
Swapped it out for a different one (I'd borrowed it from work while mine was being repaired), problem went away and never happened again.
There is zero logic I can see for this, and makes me want to throw computers down a well and live in a cave.