If you are checking the pins direct at the port and there is no change in voltage (assuming you are testing the correct pins, easy to look at the port the wrong way round) then Mach is not communicating with your port. That either means you have the wrong address or the driver is not working correctly. However as you seem to now be getting the motors holding I presume Mach must be sending a signal out through the port so it must be correct, that is assuming when you press reset the motors are free?
Hood