Brushes are the usual prob, were they worn down when you replaced them?. Did you release the brushes from their captive state?. Make sure the 2 electrical tags left and right coming from the motor windings correctly engaged with the sockets in the plastic brushplate. If all above is correct then it could be a pcb fault but often there are more than one pcb and mighty expensive, might be best to call an engineer.
Kenjo
March 2014