I previously had this problem: https://www.bleepingcomputer.com/forums/t/644460/computer-wont-turn-on/
I'm about to take my PC to a local shop, once it opens in a few hours.
Suppose they diagnose that the problem is the motherboard.
I remember when I first got this motherboard, I was advised by a local expert (who has since gone out of business, so I can't ask him) that I should only expect it to "just boot up" without a hitch if I'm using the same motherboard as before. The OS is apparently installed with a particular motherboard & bios in mind. So if I'm getting a whole new motherboard (like I was back then), I would need to reinstall my OS.
I currently have a Gigabyte GA-970a-UD3P motherboard. I understand that those come in two versions, "Rev.1.0" and "Rev.2.0." I currently have the second version.
If my problem turns out to be a faulty motherboard, could I get a Rev.1.0 motherboard and have it work with my current OS installation? Or do I need specifically a version 2?