Business PCs, Workstations and Point of Sale Systems

After just a couple of hours of normal use, our new Z2 mini G9 desktop workstation (5F0C7EA) refuses to power on being almost dead.

But not completely dead because one internal led blinks in yellow when the external power supply is connected
and then at about 10 seconds after, the front white led from the power on button blinks for less than a second too.

After that nothing happens and I mean no beep, no fan, no other led, just dead.

Things I have already tried:

a. swap the external power supply (including the power cord) with another one from an identical working Z2 mini G9

b. I tried the other way around and both power supplies are confirmed to be working with another Z2 mini G9

c. cmos reset by pressing the internal button and also by completely removing the battery

d. push the front power on button for 20 seconds or so

e. reseat the ram modules, ssd, video card and even the wireless module

f. disassembled the power on button in order to press directly

In the end I think the motherboard is at fault maybe due to a corrupt bios.

I would like to know if there is something else I can do, perhaps a special bios recovery procedure ?

I have to mention though that no peripheral works including keyboard or monitor and that the defective unit was protected at all times by an apc surge protector power strip.

I also tried to power on without any detachable component like video card, ram, ssd and so on but the issue remained:
one internal yellow blink at power supply connect, followed by a very short white blink at the front power on button then nothing.