Motherboard: gigabyte B450M S2H V2 (new)
CPU: Ryzen 7 3700x (new)
RAM: 2x16 GB DDR4 UDIMM - mta18asf2g72pdz-2g3b1ig (used from a reputable seller)
Tried two different PSUs (tested both on an old system first and that seemed to POST fine) got fan spin and no beeps (mostly, see next paragraph) but when I tried to plug in a graphics card I got no graphics output (the graphics card seem to work in a different system). Removing either of or both RAM sticks didn't seem to change anything, still no beep codes, removing the CPU power cable (the 4 pin connector) also didn't change anything.
Got something that sounded a bit like a beep from the PC speaker once but couldn't replicate that. Tried a different speaker in case there was an issue with that but it didn't seem to help.
Does the fact I don't get beep codes even when in a clearly invalid state (no RAM or no CPU power) indicate the motherboard is failed? Or are beep codes handled by code running on the CPU? I can't test the CPU or RAM on another motherboard as I don't own any motherboard with an AM4 socket or that uses DDR4 memory.
Could the power supply be faulty in some way that lets it boot older systems that might have higher tolerances but cause failures in newer hardware?
Edit: Turns out I was sold RDIMM memory as UDIMM, not sure why it didn't result in beep codes but when I got some UDIMM memory the system booted.