Question Mobo or PSU issue?

[Sepsu]

So I have a Gigabyte Z170X Gaming 7 motherboard, had it for going on 3 years now, no issues. Was running a 850w PSU with it. Last night I left my computer on like I usually do with Monster Hunter World running. Woke up to my PC at the windows login screen. Thought it was a bit weird so I logged in, turned everything back on got back in game joined a game after running around in town for about 10 minutes. Go to attack the monster and.... PC goes into shut down mode. I was like hmm... real weird. So it starts back up, gets to desktop first thing I can think of is somthing is overheating. I start up speccy to monitor the Temps everything is sitting at 30-40c which is above average but not high enough to justify turning itself off. I look up what could be causing this. Everything I can find is pointing to psu overheating which speccy doesn't show so I'm like hmm that makes sense. I decided to clean my whole PC it was dusty, so I did that then I take out the 850w put in an 800w reboot the PC, same thing Temps in speccy now 20c. When I rebooted it I noticed right before it turns itself off now the OC light and the Eco light on the board both flash sporadically then off. Doesn't even prompt the windows shut down screen anymore just full blown black and off. Sometimes it doesn't start right back up sometimes it does. Is it the mobo ? Or is the 800w I put in also pooched? ( it wasn't new ). Specs are i7 6700k, 32gb ddr4, gigabyte z170x gaming 7 mobo, gtx 1070. Computer worked fine for literally 3+ years before last night no issues like this up till now.

 

[Sepsu]

Kind of an update, so now it's not booting for more than 3 seconds. Both psu's progressively got worse to this point. Now neither boot for more than 3 seconds. That would indicate a short somewhere wouldn't it? Could a short cause all of these issues? And how would I test for a short? Can I do it with wire testers?

 

[Sepsu]

Update #3, after trying literally everything. Narrowing down a pooched hard drive, taking out literally every single piece of hardware and meticulously cleaning every spec of dust out of every little nook. I put it all back together. Still won't boot. I repeated and pasted the cpu, took the video card right out only have my m.2 and hyperx ssd in 1 stick of corsair vengeance 3200 8gb in the black socket closest to cpu. Now I'm getting fe, 19, 55 on the led post code light on the motherboard. I'm about to Crack and bring this thing in. I looked up the post codes 19 is cpu booting, 55 is memory error, fe is reserved? Literally about to put my head through a wall. It's 7am and I haven't slept. The only tiny inkling of information I can find is that the board only takes 2133mhz when the bios isn't updated. Numerous people claimed that was the fix. But the bios should be updated ? I used this setup for literally 3 years before it died.