Finally back home, I have been able to pinpoint the problem.
As you suggested, it was a memory issue.
I had installed the same pair of HyperX HX424C15FB/4 that used to work fine on both A320 and B450 ASUS and MSI boards but not on this one.
Plugged another pair of the same memory and it went on...
Thank you for the reply.
Tried more before replying.
CPU is Ryzen 3 3200G
Memory is 2 × HyperX HX424C15FB/4
SSD is Kingston SA400S37/240G
Installed a video board - no output from it either (VGA and HDMI)
Trying a new board - ASUS Prime B450M Gaming
No beep, no image, but fan spins.
If memory is removed, board beeps as it should - thus there's some interaction between board and cpu.
Tried another PSU, same symptoms.