Brake Pedal Too Firm
The brake pedal should have resistance but give under slight pressure. There are a few reasons why the pedal may firm up and not move when pressed. The first is an obstruction in the line. If a piece of rust from the brake line came loose and wedged itself somewhere in the line, the hydraulic system will stiffen up and be unable to release the pressure. Likewise, this can also be caused by a pinch in the brake line.
Another possible cause is a bad booster unit. Like a soft pedal, too firm a pedal could be caused by an issue in the booster unit that amplifies the pressure when the pedal is pushed. If the vacuum cannot release the pressure, the entire system will firm up. If it is the booster unit, have a mechanic verify it with specialized equipment and replace the part.