PC shuts down itself after 5-6 days

[kosamchetoo]

My new PC which I build 3 weeks ago is shutting down itself very strange. It's working fine, but shuts down itself every 5-6 days and doesn't reboot. After I press the power button to power it on it works fine like nothing ever happened. Everything is brand new except the GPU which I borrowed from my old PC. It's not overheating, all temps are fine.
i7 6800K
Corsair H110i GT
Asus ROG Strix x99 Gaming
Corsair Vengeance LPX 4x4GB 3200MHz Quad Channel
Samsung 850 EVO 500GB
Seagate Barracuda 3TB
Sapphire R9 270X 4GB
NZXT H440
EVGA SuperNOVA P2 850W

 

[JanHyka]

Have you checked Windows Event Log for any errors? But ths sounds more like if you had an application that is shutting it down (usual with downloaders and other long time running tools - video encoding etc.)
Do you perform anything specific when it shuts down? Can you see it shutting down (ie. is it shutting down same way like if you shut it down on your own?)

 

[kosamchetoo]

I just checked Windows Event Logger and found 1 error: The system was rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed or lost power unexpectedly. It is a Critical Level error and it's source is Kernel-Power.
No it shuts down while i'm not doing anything and shuts down instantly (like when you pull the power cord).

 

[JanHyka]

I would bet this either on PSU or motherboard then, more likely PSU. But I am far from being sure about it...
You have installed motherboard drivers right?

 

[kosamchetoo]

Yeah.