Hi Ben,

Not enough info to help I'm afraid. Need to know exactly what is connected and what isn't and to which pins etc.

Best bet is to post Pics of the Motor outputs and Inputs and outputs in Ports n pin setup in mach3.
Also what inputs your using on the PMDX and what goes to which. Also how the Dip swithces are set on the PMDX.

It will be something simple like Active low or the PMDX not enabling it's motor outputs. Something daft like Possibly you haven't enabled the Charge pump or E-stop etc.