X-axis motor doesn't turn, it's blocked all the time - how can I fix that?

Hello,

I setup Mach3 in connection with a SmoothStepper Pro. Installation of the software an plugin worked fine.

CNC hardware: I use a DB 25 breakout board (connected to the SmoothStepper Pro), a DM542A stepper motor driver and Nema 23 (23HS9430) stepper motors.

Initially Mach3 activated the emergency stop after a few seconds but that's a known problem that can be fixed by changing a Mach 3 setting - done.

Now I tried to test the wiring but for some reasons the stepper motor (I setup the x-axis) doesn't turn. It's blocked as soon as I switch the power on.

What can cause this problem?

Klaus