shutdown CPU or Motherboard cause of shutdowns?

[Auyott]

I recently built a new system (full specs at bottom of post) and it ran perfectly for three days. After that time, it began to shutdown when under heavy, graphically intensive load. When it shuts down, it will attempt to restart repeatedly for about 2 to 5 minutes before finally booting to a screen that states that the BIOS has been reset. At first, I suspected the graphics card. This was not the case, as I tried running my integrated graphics and had the same problem. I eventually swapped out every part I had spares of for troubleshooting apart from the CPU and the motherboard (as I don't have extras of these components). I RMA'd the motherboard, as I was nearly certain it was the cause. A couple weeks later, I got the very same board back from MSI and it had the same exact problem. I still suspect the motherboard, and I am about to buy a new one from ASUS, but first I wanted to make sure that the CPU could not be causing this. Prime95 runs flawlessly with no crashes, so the CPU seems safe to me. The motherboard seems to be the only cause of this issue. Should I RMA the motherboard a second time? Should I go ahead and buy a new one from ASUS? What are the chances of the CPU causing this? All responses are greatly appreciated.

 

Specs:

 

CPU: Intel Core i7-7700K @ stock speed w/Coolermaster Hyper 212X (will overclock if I can get this system working at stock)

GPU: EVGA GeForce GTX 1070 FTW ACX 3.0

RAM: 16gb (2x8) G.Skill Ripjaws V @3000mhz (ran at 2133 for troubleshooting)

PSU: EVGA Supernova 650 G2

Motherboard: MSI Z270 SLI PLUS

Storage: 1x Samsung 850 EVO SSD (500gb); 1x Toshiba 7200RPM HDD (2tb)

[Khamul]

So what happened when you tried to use the integrated gpu, it crashed.. how? how is this possible since you state that prime95 runs flawlessly?

 

If you are just getting issues under heavy load i dont think the mobo is an issue here, but the PSU or GPU. But honestly i have no idea.