Auto-shutoff at varying workloads, unknown source, custom build

[SpiderMitch]

Problem: My PC will power off (instantly not the whole "shutting down" screen) at seemingly random times, i.e. nothing running, youtube only, a blizzard game, civilization 5, basically I see no trend. Not only does it power off, it stays off, i cant turn it on again via case power or motherboard power unless I unplug the power cord, the odd thing to me is the lights on the motherboard are still lit.
Summary: Powers off instantly and randomly, will not turn on until unplugged, motherboard stays lit after power off (not when unplugged), has been reoccurring for about a month (pc lifetime over a year, dont quote me long time though)

Troubleshot: I took everything apart (except cpu inc. heatsink) and reassembled it. It worked fine (got to youtube, facebook, updated graphics drivers, and updated my blizzard games) and then it just powered off again no warning. I've also tried different outlets in the house and at a friend's apartment to no avail, I do have a battery backup (that works and hasn't been power deprived at all, cause it would have beeped) and it has been with the computer ever since I first took everything out of their boxes and built it.

Spec's:
Power: CORSAIR AXi Series AX1200i Digital 1200W 80 PLUS PLATINUM
Case: Thermaltake lvl 10 gt
MB: Rampage V Extreme (with the 3.1 card included)
CPU: i7 5930k (fan: Noctua NH-D14)
MEM: 2x CORSAIR Vengeance LPX 16GB (2 x 8GB) 288-Pin DDR4 SDRAM DDR4 2400 (PC4 19200) Intel X99
G.Card: MSI 970 4gb le
HD: 256gb ssd (win/cad/games) 4tb hd (movies)
CD: bluray read/write (ill look it up if possibly a problem)
mouse and keyboard are razer stuff

 

[amtseung]

You've managed to list every component except the most crucial one: power supply.

 

[SpiderMitch]

You've managed to list every component except the most crucial one: power supply.

haha my bad, its there now

 

[MeanMachine41]

A number of things can cause this SpiderMitch.

Assuming you have no hardware failures, you may have an unstable OC and some Bios tweaks may be required. Have you made any changes in Bios and what is your current Bios version.?
Try clearing CMOS or re-flash Bios to latest, in case of corruption.
Are all your drivers up to date.? Any yellow triangles in Device Manager.?

Do an "sfc /scannow" in an elevated command prompt, without the quotation marks to check for windows file system integrity.

There are also a series of stress tests that could reveal the culprit if you can't find a fix.

 

[SpiderMitch]

there have been a few times, when restarting (after turning it off or it turning off) that it will take me to bios screen. It is already at default settings but i will; "overclock has failed" reset to defaults, "sure?", yes, load configurations, "no settings have changed continue?", yes. And it will load everything fine. Strange thing is theyve been default the whole time as I dont know much about overclocking yet so I was going to wait till I got water cooling (dont have money for it to overheat/me break it)
as of now, when pushing the power button the fan lights will turn on (the case has blue leds), the computer (not sure what part) will "click" and "click" again a second or less later and turn off. Also all of that is after i flip the power supply's switch, after one on/off no buttons will do anything i can observe. That being said I have no knowledge or access to the other troubleshooting tips you provided.
I was able to update nvidia's drivers for my 970 last night but i dont remember any other drivers. I do have BitDefender and that told me to update nvidia's at one point (which I did) so I would assume they are all up to date.

 

[amtseung]

When you yank the power cord, the capacitors in the power supply and the motherboard still have charge in them, which is why some of your LED's are still lit.

That AX1200i is totally overkill for your system. I doubt it caused any problems.

I suspect your motherboard is dying, or your bios got corrupted after the first sudden shutdown. Clear CMOS by finding the button battery on the motherboard and popping it out. Leave it out for a couple minutes with the power cable unplugged from the power supply, then stick the battery back in and power it back on. This is the way you hard reset the bios.

Try disconnecting the CD/Bluray reader from the entire system, power and all. I've seen CD drives cause issues in the past. Unlikely, but worth a try.