rough motor

Hi all,

What could be the cause of motors which vibrates/move in a manner.
The motor was moving smoothly 2 weeks ago with the camtronics board
and desknc for dos? Now when I try it out again, the motor (on the
bench) seem to just vibrate roughly without appparently moving
anywhere, irrespective of feed rate. What should I look out for?

Thanks in advance

keongsan