you could check the AC fuse under the dash IF the electric motor does not cycle once the key is turned on-
you "might" have a silver circuit breaker located on the powermaster electric motor. if you can take that circuit breaker out and just plug the harness back in, it may turn the electric motor back on-
more than likely if the electric motor comes on and the brake pedal is hard, then it will be the black ball, or the pressure switch located on the top of the powermaster-
do you have a buddy with the same type of car that you can swap parts to diagnose your problem?
if you remove the accumulator ball, make sure that you pump the brakes up 15 time to release the pressure inside of it!!!!!!
read the directions on the lid of your brake master cylinder.
BW