Question Arc and burn when plugging in HDMI for new build.

[Kolvir]

First build in a very long time. Somehow the motherboard port cover must have become charged. When I went to plug in the HDMI cable for the first time from a powered on monitor with the system off I had a big electrical arc, burnt and melted the end of the cable, port cover and looks like the HDMI and nearby USB ports or at least the outside of them. Blew the fuse on the surge protector.

I hadn't even installed a OS yet. The system still turns on and the PS case and CPU fans still come on, but I have no idea of the damage done. I think the monitor has issues too now.

The questions I have are what could have cause the port cover to be charged? I took a multimeter to it and it was reading 120v AC, but didn't hurt to touch it(I had touched it before I knew there was anything wrong, not after the arc). I would have thought some kind of short would have been DC, not AC? idk How do I go about testing the PS and motherboard from here? I don't have any spare components. This was to be a specific use case business PC and my system is an old and heavily upgraded Mac Pro, so I can't swap any parts.

I believe I had the stand offs and everything installed ok, afaik. Where do I look and test to see what caused this? Could the PS been faulty and need a warranty replacement? Or could it have been the MB? I don't know where to start first.

ASRock B450M-HDV R4.0

EVGA 400 1 PS.

 

[RememberThe5th]

Replace that psu, its leaking voltage, Im quite suprised that it did not trip the breaker, also test the earth wire if its acidentally connected to the AC or other component in your house might be leaking voltage(if its shows 120ac as your first reading, try to find if other household is leaking voltage , stove and then the water heater ).

Also if possible if you can test psu in another house to rule out your house wiring?

 

[Kolvir]

How do I go about testing the PS by its self?