Upgraded 2009 Mac Pro won’t start

i recently upgraded my 2009 4.1 with a 2010 12 core processor tray, 32GB of RAM and a Sapphire Radeon Pulse RX 580 8GB. The first card went bad but the second has been okay, so far. I have 2 monitors, an HD Apple and a Wacom Cintiq.. it’s running High Sierra.

Today, while I was browsing, the screen went white (the Cintiq screen went blue). I immediately shut it down and tried to restart in safe mode. Nothing and no sleep light. I looked up info on what to do, unplugged all peripherals, and tried unplugging the power cord, holding the power button for 10 secs, and replugging. Nothing.

I held it down again for 10 secs, unplugged the power cord, waited 10 secs, plugged it back in and it didn’t start but the red led OVTMP CPUB lit, steady. I’ve tried restarting, but it only clicks, nothing happens, then I have to hold it down to shutdown click. I unplugged again, the red light went out, plugged in again, no warning lights. When DIAG LED is pressed the 5v STBY lights up yellow.

Any ideas? I thought it might be the power supply, but I’m not sure. Would that cause a white screen if it went out? Could the video card have gone bad again? Thanks in advance for any help!