PC random reboots during gaming

Hello,

I bought a gaming PC from Amazon 2 years ago, and the following issue has always plagued my computer.
The PC reboots on numerous occasions such as if I'm watching a YouTube video, or using Chrome and Spotify at the same time, or even Chrome on its own. It happens most frequently when I launch a game such as Fortnite or Overwatch, sometimes even if the PC is idle and no processes are running in the background. Specifically, the whole PC restarts, fans turn off, lights turn off and within a second it turns on again and reboots from scratch. There has never been a warning or BSOD.

These reboots are frequent nowadays and very random, sometimes I can play Overwatch for hours with Discord open in the background and it will run perfectly. Other times, I could be turning on the PC and it will restart 2 or 3 times while it TURNING ON.

This problem has worsened in the last few months as at first it only happened once every few days or so and I just ignored it, nowadays it sometimes reboots even when I turn it on.

To try solve the issue, I have re-installed Windows (the first time I unboxed the PC and tried installing Windows for the first time, it rebooted several times DURING Windows' installation.
I ran stress-tests suggested by the Internet such as Prime-95, Heaven, Furmark, OCCD. The PC passes them all with 0 errors, so this is very puzzling. All the drivers are up to date. Temperatures are also pretty standard when idle and when under stress.

I have not replaced any piece of hardware since I do not wish to waste money on a component and have it not resolve the issue (I have read forums where some people with similar issues have replaced several components and problem still persists).

CPU: AMD Athlon X4 860K
GPU: Inno3D Nvidia GTX 1050
PSU: CiT ATV500W
Motherboard: Gigabyte GA-F2A78M-HD2

Please help.

Edit: I have also tried performing a clean GPU driver update and other solutions on forums that have helped people with the same problem, none have worked for me.