Before anyone screams, "PSU!" I'll say, I have replaced ALL the hardware. Okay, anyway ...
The PC in question is a home built that I've had for many years. At some point during the past year, it began randomly shutting down (as in pull plug from wall style, not BSOD and not reboot. Shut down BUT internal power light remains on). I checked all the typical culprits: power supply, ram (memtest), video card, monitored CPU temps, nothing out of the ordinary. So I systematically began replacing parts. The first to go was the motherboard as I DID feel there may have been a crack in it. Sometimes simply tapping the desk would cause the PC to shut down, which is why I went that route before the PSU. So with the new mobo I went with new RAM and followed with a new video card. Still shutting down. Replaced the 7200 RPM HDD with a SSD (boot times cut IMMENSELY! If anyone doesn't have a SSD, I can't recommend it enough! But PC still shut down - eyeroll). Changed the 600 watt PSU with a brand new 750 watt, just in case I was now under-powered (though everything showed that 600 should do fine). First try, PC shut down. Finally, I replaced the CPU (same one: AMD FX-8350 black edition). When I pulled the old one I noticed it had a couple bent pins .. thought maybe that was an issue? Made sure the socket was clean and clear and popped the new one in, greased and put on the heat sink and fan (not stock cooler, aftermarket similar to Coolermaster Hyper 212. Been using Core Temp and hasn't gone over 50C. The shutdowns persist. So tonight I began pulling memory sticks to check for bad ram. All checked out okay .. or, all are bad? Shutdowns occurred each time. I've found a way to duplicate the failure consistently: Start Steam, run Arma 3 .. crashes just after loading screen goes dark and before "APEX" screen comes on. Temps looked good all the way. It shuts down at other times. My daughter will be playing Sims3 and it just randomly shuts down, no consistent trigger. She may be playing minecraft all day and no issues .. then something will cause it to shut down and rest of the day, it's hit or miss.
All that said, there is one thing that is different. Windows 10 - I used to have Windows 7 before putting in the SSD. God knows I HATE Windows 10 for many reasons but, the shut downs WERE occurring before that switch as well. I'm just about at my wits end here as to what's causing this. Anyone with ANY thoughts (legit of course, not smarta$$ like, "Buy a Mac") are greatly appreciated. Oh and, I neglected to say this cause I feel it goes without saying but in case some wonder, yes I have all updated drivers and Windows updates. And with the SSD came a full and clean install of EVERYTHING so this is basically a brand new computer but still suffers from the shutdown issues so I'm completely baffled.
AMD FX-8350 Black Edition 4.0 GHz
Gigabyte GA 970-A DS3P Board
G.Skill Ripjaws X Series DDR3-1600 4GB (x4)
XFX Radeon RX580
Sandisk SSD
Thermaltake 600W PSU / Corsair CX 750M (shut downs with both)