My PC Mystery: A Tale of Random Shutdowns and Troubleshooting Woes

So about 6 months ago, my PC unexpectedly shut off while I was playing a game. At first, I didn't want to touch it too much, afraid I might make things worse. But as time went on, the problem persisted. Normally, when I boot up my PC, the fans would rev up to maximum speed, then settle down to normal. However, after that initial shutdown, the fans would spin at normal speed, but the PC wouldn't post. The fans and lights would come on, but it just refused to boot. Frustrated and determined to solve the mystery, a couple of days ago I mustered up the courage to dig into the guts of my PC. I meticulously went through all the wiring, double-checking every connection, and even reseated the CPU. I also cleared the CMOS, hoping that would do the trick. But to my dismay, when I pressed the power button, my PC remained lifeless. No fans, no lights, nothing. I suspect the culprit could be the motherboard, but I want to be certain before I invest in a replacement. It's a frustrating journey trying to troubleshoot and fix PC issues, but I'm determined to get to the bottom of this. Have you ever experienced a similar situation? Any advice or suggestions would be greatly appreciated. Thank you for taking the time to read my PC mystery. 🙏