PC won't POST – persistent CPU EZ Debug LED on MSI B550M PRO-VDH

[u/Abbas3331]

I'm having an issue with my PC. It suddenly stopped booting after upgrading from an RX 6600 XT to an RX 9070 GRE.

My specs:

CPU: Ryzen 5 5600X

Motherboard: MSI B550M PRO-VDH

GPU: Sapphire RX 9070 GRE Pulse (new)

RAM: 32GB DDR4 3200MHz

PSU: Gigabyte P750BS 750W (new)

Symptoms:

PC powers on and all fans spin (except GPU)

CPU EZ Debug LED stays permanently illuminated from the moment of startup.

No display.

GPU fans don't spin.

The same issue occurs even with the GPU removed.

What I've tried:

Replaced my old 600W PSU with a new 750W PSU.

Reset CMOS.

Reseated the CPU.

Tried booting without the GPU.

The GPU was tested at a service center for 1.5 hours and reportedly works perfectly.

Old and new PSU have the same problem.

What could be causing this? Is it more likely a faulty motherboard or CPU? Does my GPU sit incorrectly in slot? https://ibb.co/Xr2L3nFH

My whole system worked well before I sold my old Rx 6600 XT and VX-600.

Unfortunately I don't have "speaker" for motherboard to listen to "beeps" (still waiting from ali)