It is surprising how a supposedly intelligent person can be so incapable of managing such things.
My own brother-in-law, who is an engineer btw, tried last year to self-upgrade his PC. He bought all the right components, motherboard, CPU, RAM, cooler, SSDs, etc, and put everything together.
When it didn't work, he called me, because he knew that I have extensive experience in upgrading my hardware. I tried to diagnose by phone what appeared to be a RAM problem. We tried removing all but one stick, putting the sticks in different slots, all to no avail.
Bereft of ideas, I asked him to remove all the DIMMS and try to boot. We got the same error, ergo it was not the RAM. At that point, I pointed him to a very good PC Repair shop because, if it was the motherboard, I didn't have any other solution.
It turns out that my brother-in-law had put the CPU in wrong. Which means he forced it in, because slotting in CPUs these days is as easy as just gently dropping it in place. All you need to do is align the marked tab on the CPU with the tab on the motherboard and drop it in. But no, he put it in wrong, forced it down and screwed the cooler over it. Obviously, the CPU was dead and the motherboard as well.
When I learned what had happened, I was speechless. But, that is how it is. He's far from stupid, but boy was he stupid there.