There is 2 different reasons that I know of that will cause this malfunctioning. The most common reason is a worn out coupler. The coupler is a small round piece of plastic that connects the opener motor to the screw contained inside the rail that spins and moves the trolley forward and back to open and close the garage door. This small piece of plastic connects two pieces of metal so when the opener is put under extra stress like a broken spring on the door or just years of lifting a heavy or unbalanced garage door. Eventually the coupler will get stripped out and the motor will spin and the screw will not. This is an easy fix and it only takes a few minutes to replace. The coupler itself cost about $2 dollars.

older Genie models

The other reason for this malfunction is on older Genie models that use a clutch system to control the pressure that the opener puts to the garage door. This is easy to identify because the opener unit has a big screw with a plastic nut at the end of it. This screw sticks directly out of the back of the opener. When the plastic nut is tightened up it allows the opener to put more pressure to the door and loosening it obviously puts less pressure. When these clutch systems deteriorate they will fall apart and pieces will fall out its a big mess. This will also have the same result as a worn out coupler. The motor spins and the screw will not. This older model clutch malfunction can not be fixed so just replace the unit.