Windows 10 PC randomly shutting down without warning

I haven't had any shutdowns since I followed the stuff on the first responses instructions. Time will tell if it continues to happen. I had updated my GPU drivers, but just praying that it's not my PSU as that's a much more frustrating thing than a driver update or windows setting change

The good thing about PSU, is that they either work, or they dont.

Id say its a mix of GPU driver and putting your power setting on high performance.

You had some feature or setting somewhere that gets the bright idea to save you power if X. Which turns of windows most of the time :p.

Well it did happen twice again last night so now I'm even more convinced that it's hardware related which is a massive bummer

and now 3 more times after that, too. I've reset all BIOS settings, I've tried checking all my drivers, I updated every driver I could, I checked event viewer and nothing shows up, my temps are good, my GPU is reset to stock clock, I uninstalled Rivatuner to make sure it wasn't an issue with overlay, I turned on high performance power mode, disabled sleep, disabled HDD sleep, ran a RAMcheck (everything was fine) I checked all my drives for errors and found none, I made sure I was on the latest windows update, latest GPU driver, latest BIOS driver, I disabled fast startup, monitored temps, cleaned the entire inside of my case carefully, I checked for leaking capacitors. 

I'm at a loss here. I don't have the funds to replace anything and I feel like I've exhausted all of my options and can only imagine that it's either Motherboard or PSU failing now.

Okay, so, some updates. 

I have since used a different GPU, and had the same results. Tried both GPU's in different PCI-E slots (one at a time, though, not SLI'd) 
I tried the RAM 1 stick at a time and made sure it was slotted correctly, I tried disablying my 144hz monitor and only using my 60hz, I did a completely wiped and fresh install of windows. All of these resulted in the same issue: 

Loading any game (haven't tried other programs yet, as I don't really know what to try) results in a complete instant shut down. No messages, no errors, nothing. Just suddenly off. 

Everything was working fine 3 days ago and nothing changed, but suddenly it was shutting down in the middle of games, and now it's just moments after I load it up. 

"can only imagine that it's either Motherboard or PSU failing now. "

- It certainly looks that way.

A psu will function when faulty, until you put a load on the system. It only takes a very small drop in voltage output on the +12V rail to

cause issues such as yours when you put the system under the load of a system intensive game.

There is also potential of a faulting  PCIe circuit on your motherboard, which could affect all PCIe slots.

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I had considered the PCI-E issues, however I moved my GPU over to the second slot and everything was exactly the same. Boots normally, uses chrome and discord fine, but crashes midway through loading a game. 

Even if it was the PCI-E slot(s) going bad, wouldn't that just ultimately wind up turning off my display while keeping the system running? I know I can boot without the GPU slotted, but obviously I don't get any video since I don't have onboard graphics. 

Is there anything else I should try? I was considering trying out a GPU testing software like unigine just to see if it shuts off on high impact usage, or if it's specifically something to do with games. 

I have 2 SSD's, one is a 120gb Kingston SSDNOW V3.0 from ages ago, the other is an A400 model Kingston. Both appear to be fine when checked for errors and my HDD is just a backup/spare and I was running the system earlier without it plugged in just to make sure that wasn't it, either.  

Edited to add: I would like to test my girlfriend's PSU, however I need to try that another time as when I built her computer, I took pretty good care to snake and tighten down all of the cords to keep it clean looking and my PSU is not modular so i would need to be able to carefully remove all of her cables, and mine, and then test and it would be a real pain to get hers back together and looking clean again. 

"wouldn't that just ultimately wind up turning off my display while keeping the system running? "

- Oops ! Yes, most likely, but if there is a short, or maybe a dry solder joint somewhere in the PCIe you could get random shut downs.

With all you've done, it's not looking good for the psu though.

- If the gpu you tested with is a known good gpu, testing your card shouldn't be necessary, but I won't hold you back :)

More long shots....

- If you haven't already, see if  - Crystal Disk Info  -  flags any of your C:\ drives parameters.

- You may also want to try using another SATA cable on your C:\ drive. Particularly if the one in use has a sharp bend in it.

- What about the power switch on your case ? They have been known to short, or get a loose connection now and then.

- I've only done this once, but it's only half as painful. If you decide to test the psu, you don't have to remove your psu to test the other.

Just unplug everything, and leave the side off the case. Set the other psu on it's side next to the case and connect.

Maybe save your girlfriend some downtime and test your psu on her machine ?

- Have you been getting any crash dumps with these random shut downs ?

-  DCOM errors are pretty common and generally not meaningful.

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Alright so I was able to finally get my partner's PSU out of her computer and dropped it into mine. Ran and gamed for 50 minutes or so without a single issue, so I think we've effectively answered the question. Unfortunately not the answer i was hoping for (was hoping it was something software related and a free fix lol) but glad to know that it *IS* fixable at all. 

Thanks everyone for the help and the suggestions