I have a Craftsman Liftmaster 41A5389B. Last night my daughter pulled the red cord that disengages the door because she thought it was a light switch. Unfortunately, my opener will no longer engage. I've pulled the cord back into it's horizontal position. Using the wall unit or the remote, the chain moves but the part won't click fully into the housing and engaging the opener. This is a new problem I haven't encountered before. The springs are pretty new (replaced about 18 months ago) and there is nothing blocking the sensors. I cleaned the sensors for good measure though. I took a close look and I see no problem with the chain or the trolley. Can you help?