Why doesn’t my HP Pavilion 590-p0318ng POST?

I had this PC (HP Pavilion 590-p0318ng) before buying a new setup. I only used the CPU, RAM and GPU from this PC.

Specs were: Intel i5-8400, 16 GB DDR4 2666 MHz and a GTX 1050 Ti.
These parts are now installed in my setup that runs perfectly!

Basically now, I want to revive this PC for home office purposes.

I reinstalled a CPU (tested Intel G4400 and i3-8300) and a 4 GB DDR4 2133 MHz.

As soon as I plug in the power cord, the PSU and CPU fan spin, but nothing more happens. No beeps, no signal.

My last test was with another Intel i5-8400 (maybe because the BIOS had whitelisted CPUs), but still no success…

All the tests were performed with almost nothing connected, not even the front panel.

Is it a dead motherboard?

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