i drive a 2000 cavalier, automatic. last night i parked on a hill, pulled the e-brake, and the car started rolling back. i let off the e-brake and let it roll onto flatter ground, but the key wouldn't turn, the pedal brake was locked, and the steering wheel could still be moved even though the car was in park, although it was very difficult to turn. on flat ground the car would not stay still unless i had the e-brake up. after about ten minutes, i went out and tried to start the car again and it worked, everything was fine. any idea what might have happened?

sounds like your ebrake is not working. The car will not let the key and steering work if the car is in park. The foot brake should still work but since it was in park there was no vacuum assist for it so its harder to brake. Perhaps the ebrake is gripping a bit but not enough.

try replacing your shoes/pads and free up any sticky parts. depending on the model you have. maybe your cable maybe be stretched