Question PC randomly reboots and goes into a restart loop with no errors or apparent causes

Sep 25, 2020
I built my PC a couple of months ago, back in April. Not too long after it would occasionally shut off with no warning or error and then reboot. Didn't think much of it then, since it was reasonably rare. However, in August these resets started happening so often, that the PC became unusable (every 15min or so) and eventually became so frequent that Windows couldn't even fully load in before a reset would occur putting the PC into a restart loop.

List of components: AMD Ryzen 5 3600, Asus Prime B450-Plus, Asus Nvidia GTX 760 DirectCU II, Cooler Master Elite V3 500W (later changed to Be Quiet! Pure Power 700W), Kingston A400 240GB SSD, Kingston HyperX Fury 16GB DDR4 (2 sticks) and Seagate BarraCuda 1TB hard drive
All the components brand new, save for the GTX 760, which was in perfectly working condition and I was planning to upgrade it at a later date.

Originally I thought this to be caused by a faulty or underpowered PSU, but after upgrading the issue persisted. I have also attempted to reinstall Windows after formatting the SSD and bringing the motherboard and CPU for warranty repair/checkup (they found no issues with either). Back when the PC was usable I preformed a CPU stresstest (didn't cause a reboot), temperature test (CPU temperatures of around 86C didn't cause a reboot) and did a Memtest which also found no issues. There was no BSoD or error messages upon the PC shutting off or starting back up. The only entry in the event log about it was a critical error with EventID 41 stating, that PC was powered off incorrectly. After swapping PSUs PC booted up and worked for about an hour before shutting off and going into the restart loop. The PC does not shut off when in BIOS menu.

This is my first post here, so I'm sorry if I did something incorrectly. I'm just somewhat desperate at this point and hoping to get at least some sort of clarity about what might be the cause.
Thank you for your time.