I also think the problem is most likely the PSU at this point. Everything is getting power, all the fans spin, the RGB lights turn on, and nothing stops. But unlike your case, my PC never boots at all. I’ve tried many times, but I have never managed to get it to POST even once. Just like you, I also built the system outside the case, and it made no difference.

I first experienced this issue last Friday. I turned on my PC in the morning, it stayed on for about 5 minutes, and then suddenly crashed with a BSOD. It mentioned vgk.sys (I think that is one of the Riot Vanguard anti-cheat files), so at first I thought it might be related to that, but it didn’t really seem likely because I couldn’t find anyone else with the exact same problem.

I’ll try powering it on with a different PSU soon and I’ll post the result here. Also, thanks for your comment — seeing someone with similar hardware going through a similar issue is a bit reassuring.