You mentioned a buzzing in another reply. That sounds like a grounding issue to me. Any chance you blew something under the board that is causing a short? At this point it would be wise to do a full tear down.

I’m almost at my train stop, so one final question before disappearing for the day: when resocketing the CPU did you put it in correctly and was there damage when you removed it initially?

Is the power switch on the PSU flipped on? Are the front panel wires seated in the right places on the motherboard?

Those are the two that get me when reassembling. I used to have an asrock 320m that had absolutely no grip on the front panel wires and it was easy to unseat one when blowing air into the case.