Chamberlain Powerdrive PD422D 1/2 HP Security Plus Screw Drive Garage Door Opener "garage door closes halfway" Questions

...garage door opener doesnt close all the way. I hit the wall switch and the remote and I get the same result, the door goes down about 3 feet, stops, then reserves itself. The lights on the opener do ...

...garage and stopped it halfway as i only wanted it to stay half open to allow ventillation. It made a horrible noise. now the drive limits got erased. I've tried to adjust the limits with the screws ...