Random Restart in BIOS

Matqo

Honorable
Dec 30, 2013
12
0
10,510
Hi all,
I have recently decided to go for upgrade and built my 3rd gaming rig.
However the PC restarts completely randomly from within Bios, Safe Mode or the OS (Windows 10)
The specs are:
GPU: GTX 1080ti Strix OC
CPU: i7-8700k
RAM: G Skill Trident Z 3200 CL14 (2x8gb)
Mobo: Asus Z370 Gaming F
PSU: EVGA G3 750W (Gold rated)
SSD: Samsung Evo 850 (500GB)
CPU Cooler: Corsair H100i v2

Initially I assumed that this could be of the GPU, however after removing it from the build and using the onboard (i7) GPU the results were exactly the same. 

I have then presumed that PSU could be a culprit and took an Corsair CX750M (750W) PSU out of my old rig and used it, again without any change to system stability. 

Next was the ram, Tried one DIMM (8gb) in each of 4 slots, detected but no change on stability.

The overall system performance is great however, I was able to play Assassins Creed Origins for about 2 hours (70fps max settings at 3440x1440) then after turning the game off and leaving system idle for half an hour it restarted. The system appears to be most unstable when running memtest where it crashes/restarts after running through 50% of the test.

At this current moment I'm assuming that this could be caused by either the Motherboard or the CPU however after running prime95 for about hour and having the CPU loaded to 100% the temperatures jumped to 70 degrees C about once, then went down to 53 and stayed like this for an hour at which point I turned the test off as it seemed pretty stable. 

All help will be appreciated, I'm literally running out of ideas about what could be wrong with the system at this point. 
Thanks

TL;DR: Brand new build, tried 2 separate PSU's (750W), each ram stick in different DDR4 ports, Removed GPU yet system reboots even in BIOS.. Is my MOBO faulty?
 

Matqo

Honorable
Dec 30, 2013
12
0
10,510


I've updated the BIOS via the web-update option from within bios.. I've pretty much checked everything at this point, later on today I'll disconnect all LED's/case fans etc in order to isolate the problem to just the motherboard or CPU.. However the Load Test was really stable therefore I don't think a problem is in the CPU. Using Corsair Link software I was able to observe that Temperature sensor 5 readings jump from 0º to 127º but I'm unsure whether that is a peripheral sensor or an actual fault in the motherboard.