I have Genie opener. The door will not open at all when closed. The motor runs and the drive bolt spins, but all that happens is the carriage rattles and stays in place. When I release the carriage and manually open the door then lock the carriage, the door operates with the opener(closing) but, last 2/3 ft the carriage slips and the door falls all the way. Springs not broken, hinges apear o.k. 1st time working on a garage door. Anyone help?