If the door simply stops short of the floor the likely culprit is the down limit switch.
Setting garage door to manually opening.
Keep the rollers and chain lubricated on your garage door.
This will reengage the door to the opener system and now the only way to open and close your garage door would be with the power of your opener unit.
Consult it first before tinkering with your door.
To manually open most garage doors you simply pull a corded handle that is attached to the door.
To reset it begin by pulling the cord in the opposite direction.
Many electronic garage doors come with a bypass switch allowing you to override the system and manually lift it open when needed.
To reattach your garage door to opener system you ll pull the emergency release cord down and towards the opener.
Have a helper steady the ladder.
This emergency release cord will be attached to the trolley in the center of the garage door.
To locate the bypass switch look for a red rope hanging down from your garage mechanisms.
Diagram of garage door engaged and disengaged to screw drive opener system.
This disengages the electric drive from the door and you can manually open and close it.
It makes the door operate quiet and makes the chain and all.