To me the whole thing sounds like a hardware issue. Considering you already swapped the PSU, that leaves mainboard, GPU and drives - and technically also CPU, but that's unlikely the culprit.
I'd start checking all cables, unplug and replug everything, including the case front panel headers, you know the tiny cables connecting the power button and reset button etc. Also make sure that the mainboard is seated correctly, i.e. nothing is shorted at the back due to a standoff or something. And check in Windows Event Viewer if the event log contains relevant warnings, apart from the usual "Windows wasn't shut down properly".