Question Nothing happens when turning on: Gigabyte Z390 AORUS MASTER dead?

Jan 7, 2020
MOBO: Gigabyte Z390 AORUS MASTER(rev.1.0)
BIOS Ver. F6? (not 100% sure, cannot boot to check)
GPU: onboard
CPU: Intel Core i9-9900K (BX80684I99900K)
Memory: Corsair DDR4 3200 64GB
Power: Seasonic Prime 850W Titanium
Operating System Win 10 64-bit

Hi guys, I am new here but pretty desperate now hoping to get some thoughts: really appreicate any inputs!

So this PC has been running alright for more than a year, until yesterday I changed some BIOS configs.

The change is very regular since I moved the Intel Optane memory to a different M2 slot, therefore the BIOS SATA config has to be re-adjusted accordingly. The Optane memory has been disabled in Windows before it was pulled out (to avoid data corruption).

And there is no overclocking or BIOS upgrade/flash activity going on when the issue took place.

Symptom: Cannot boot, cannot even see POST or enter BIOS;

-After plug in power cable and turn on PSU switch:
--The LEDs on AORUS log and ESS block flash once instantaneous and goes off
--The LEDs of "Power" and "Clear CMOS" buttons on the back IO plate turn on and stay on

-Press the power button to boot, nothing happens:
--No LED lights on MOBO at all;
--No fans running at all;
--No beep;
--No display on monitor;
--Absolutely nothing turn on or show up, as if the power button was never pressed.
Therefore there is no POST message, and I cannot even get into BIOS.

What I have tried so far, but didn't work:
-Long press the power button and/or reset button
-Press the
-Clear CMOS (both pressing the button on the IO plate and jumping the clear CMOS pin);
-Remove the battery;
-Switch to the backup BIOS;
-Take the board out of case;
-Reduce the devices to only:
--one RAM bar
--one SSD SATA with the booting OS
--onboard GPU (which was how it was before the issue happened)

What I have ruled out and confirmed:
-The power cable is well-connected and has power
-The PSU is good and with enough throughput (850W). And I tested with another less good and weaker PSU, still got everything the same
-The turn-on/power button is indeed pressed:
--pressed the front power button per usual;
--pressed the power button on the IO plate;
--shorted the power pin on MOBO;

PLEASE help! Thanks so much!