Stepper motors will just vibrate if the wires are not in the right order. Not sure what order to suggest in your case, but try swapping the pairs of wires. The coils generate a magnetic pole that spins the motor, and if the poles don't 'charge' in the right order, it just vibrates.
There is a animated graphic on wikipedia that illustrates what I am trying to say:
Stepper motor - Wikipedia, the free encyclopedia