Why does my computer randomly restart?

Question

Computers

Purchased new components motherboard, processor and memory. I installed all the new hardware in my computer. It started with a bang, even Windows 10 did not have to be reinstalled. But after stress testing, my computer began to spontaneously reboot. After rebooting, I looked into the BIOS, the temperature of the processor was 40 degrees.
Observations
It does not just reboot, but turns off for 1 second and starts again. This usually happens when I do minor activities (surf the internet). If I play games I haven't had crashes (yet).
In normal tasks, the percentage does not heat up more than 50 degrees, during a stress test it reached 89 degrees in 4 minutes (I think you need to change the cooling later)
Reflections
I did not change the PSU, but it should have been enough for this computer at 700 W.
I did not take the RAM as a set, I took the same two strips of 8 GB each (although they have some kind of wavy contacts, but it starts up). In principle, new motherboards should not have conflicts.
The feeling that it reboots due to downtime, because I set download gta 5 for the night (I have a weak Internet) and the computer crashed only after a full download and installation.
Any guesses?

Answer 1

even Windows 10 did not have to be reinstalled

really, why does it reboot?
It can't restart spontaneously, probably because of BSOD
https://answers.microsoft.com/en-us/windows/forum/...