8160w 8160wb 8165w 8164w 8155w.
Manually close liftmaster garage door.
It should move smoothly and only require a little force to open and close.
Now press the remote control.
Once the lever is disengaged you should be able to open and close your garage door by hand.
If you pull the emergency release lever while the door is open you can cause the garage door to shut rapidly.
A word of warning.
Liftmaster garage door opener models 8160w 8160wb 8165w 8164w and 8155w.
To reconnect the garage door to your liftmaster garage door opener manually close the garage door pull the emergency release handle down.
This will cause the trolley to move into position and reconnect to the garage door.
These steps should fix most doors.
In this post you will find downloadable links to all models of liftmaster garage door opener manual.