[SOLVED] Random shutdowns with no pattern

Jun 1, 2020
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Hello,

I am currently having a situation where my PC randomly shuts down for like 2-3 seconds, everything stops inside, and then it powers back on by himself.
Current spec is:
Intel i5-3570K
Asus ROG MAXIMUS V GENE Motherboard
Noctua NH-D14 CPU Cooler
HyperX Fury Blue 8GB, DDR3-1600MHz, CL10, Dual Channel
NVIDIA GeForce GTX 660 OC WINDFORCE 2X, 2048MB, GDDR5, 192bit
2x 1TB Hard drives
1 SSD Samsung 850 EVO 250 (on which the OS is intalled)
Zalman ZM 600-LX
4 case fans, one of them being in the front and it's a bit bigger

I found no particular pattern in the shutdowns, it happens when I'm gaming, browsing or even idling desktop. The inside is clean, as I periodically clean it.
What I have tried is changing the RAM sticks on the other slots, which made it alot better, reducing the shutdowns to like once or twice per day, maybe not even that. In the past, it was like shutdown after shutdown, maybe 10 times in an hour.
I also changed the thermal paste from the CPU, thinking it might be something from overheating. Apparently it's not.
I am not playing very intense graphic games.
Other things I have tried were changing the slot of the graphic card, unplugging and plugging back all the connections on the motherboard and on every component.
I even tried with an UPS, thinking I have some small powercuts, but with no avail, it still happened.

Also, I forgot to mention that today, when I tried to do system rating calculation from windows, to see what rating I have on current spec, it crashed immediately when it was trying to do 3d ALU Assessement. I repeated it, to be sure it wasn't random and it turned off again, making me think it's a CPU related issue, maybe?

Maybe someone here can give me a hint on what to try next.

Thank you in advance!