Why is the brake petal on my bronco so stiff not able to use my brakes at all

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Was. On freeway doing 65 I needed to make a sudden stop but my brake pedal did not move at all turns very stiff had to coast to a stop on shoulder. This happend to my wife three days ago but then brakes went back to normal now it happend again can't take changes baby on board .also when ever we would brake for example on a red light towards the end before coming to a full stop you can hear a humming noise whith vibration then the truck would pull to the left then it would stop..items replaced brake calipers brake booster still having this problem..