@AstroDoug Please post your config.g , so we know what speeds you're trying to move the motor at. Also, has the motor worked previously? Have you tried connecting another motor to the Y axis? Have you tried connecting the motor to a different axis? Does the motor do anything when you try to move it?

However, most likely is that there's a wiring problem, and either the motor has a loose wire connection, or is wired incorrectly. Test the motor, ideally with a multimeter, identify the phases, and check the plug is wired in the correct order for the Duet. See https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors#Section_Using_the_internal_drivers

Ian