While switched off at the wall not unplugged so it remains earthed. Unplug the sata cables either from the drives or the motherboard itself and re-boot . If it stays on it’s a SATA cable plug them back in one at a time switching off at the wall every time you plug in or unplug anything . By process of elimination you can find the offending device/ cable. Take pictures so you know where everything goes. Keep repeating the process until there’s nothing left to try. At which point it’ll probably mean you need a new power supply.