Is the booster working.
I test mine by pumping the pedal a few times before starting the engine to vent any vacuum then push on the brakes and start the engine , as the engine pulls a vacuum the brake pedal should creep to the floor slightly.
The other possibility is the slides on the calipers have stuck or seized (quite common).
Another possibility is a stuck piston in the brake master cylinder . If the front dips when you stab the brakes the hydraulics are working.
Just a few things to try