24V is being supplied at the input but isn't seen at the pins of the DCDC power module. The most likely cause for this is that the rectifier diode is the wrong way around. This triggers the short circuit protection when the voltage supply is correct - the diode creates a short circuit between 24V and ground and causes the polyfuse to activate, stopping any voltage going to the rest of the board. To fix, reverse the diode on the PCB.