My 3700x did the same thing ".54GHz" and then shut off. This occurred twice before I could figure what was happening, which was the cpu was thermal throttling at ~100C. I swapped out my AIO cooler for the stock amd air cooler and my system will no longer post, let alone turn on by power switch or motherboard power button (motherboard lights would turn on by flipping the psu power switch but no fans, no other lights, no pump sounds, no hdds spinning up). "Cpu was never removed from the socket." I am currently testing for the cause but I believe that a faulty cooler burnt out my cpu but I have no feasible way to confirm that.
Edit: It was the motherboard (x570 Taichi), I had it tested at Microcenter. Cpu and cooler still work fine. I do not know why this happened though.