Thank you for the reply. Maybe I did not explain myself very well.
If you hear two beeps, it means that board is booted up.
Not necessarily, we hear the two beeps, but the board is stuck at "Starting Services".
Try to change baud-rate, use 9600 or 115200, even better if you try MAC-Winbox to access the board
We have serial access to the board and can access the boot menu etc. We can watch the board start booting up. The problem is, after the two beeps, in the serial console, it hangs after the serial console prints "Starting Services". Winbox is of no use at this point, the board does not respond to Mac connects. When we use netinstall to reflash the firmware, in the serial console, after it creates the RSA keys, it then beeps twice and hangs again after printing "Starting Services". We have tried flashing 2.9.46, 2.9.51, and then back to 3.1.0, still no go.
Is there a way to downgrade the bios or bootloader from 2.15 back to 2.14 or something else? Is this possible using the serial console boot menu?