Mercruiser 120 drive problem

[Sjharleymc]

Hi I am new to the forums. Just bought a 69 starcraft with a 120 inboard outboard. Took the boat out for the first time today. When we had the motor idleing we could hear a vibration and the boat was not wanting to reverse. I tried to put the boat in gear to leave the dock the vibration was gone but the boat would not move. Tried forward and reverse but nothing happened.
Not familiar with these at all so any suggestions will help. Thanks