HP Z400 not turning on..

Hello Everyone,

As the title suggests my hp z400 is not TURNING ON for even a second. When i press the power
button, only the GREEN HDD LED turns on for a second or less and then it SHUTS DOWN again.
And there is also no POST BEEP or any ERROR CODE BEEPS.

Things i have already tried, btw i only have a single RAM stick inserted right now and everything else removed.

1) Tried removing everything including GPU, HDDs, SSD , RAMs.
2) Tried resetting the BIOS using BIOS switch.
3) Tried changing the PSU, with no success.

The only thing left i think, is TURNING ON the PC by shorting the pins on board, plz guide me on how to do it on HP Z400,
as the FRONT POWER button might be the issue.

Any other suggestions are highly appreciated as well.

Thanks.