Redbrickman
Printer Master
Good news, I have always found them quite helpful, one of the better suppliers from that neck of the woods.
I would guess that the printer is tripping the PSU's overcurrent protection when the printer is warmed up.
physically disconnect your heated bed and see if that cures the problem
When does you new control box come?
For a guy who said he didn't want to get too hands on in building a printer, you sure have gone deep into the rabbit hole!
Do you mean the power supply was supplying power to the motherboard as you plugged in the motherboard? I would advise against that scenario to prevent damage or injury.If I had my ATX PSU already plugged in and running, and then tried to connect it to the board