As mentioned above.. Check the bolt and nut that goes thru the square bar in the front basement. Sometimes the nut starts to rotate off and gets caught on the motor casing. You will see it in one of the following photos.
I would call Lippert and get a new motor and gearbox. My gearbox was broken so I needed it. If you can raise the jacks manually the gearbox is most likely ok.. It should be hard because of the motor. The motor and gearbox are not expensive. You might call Dave Brice @ Lippert (866) 524-7821 X-6068
davebi@lci1.com. You will also need your trailer make and model, Date of purchase(DOP) and date of delivery (DOD).
You can remove the Motor and Gearbox by taking out two bolts which are diagonal. There are two other bolts that hold the gearbox on the motor. By the way, the motor has a smaller gearbox built onto it. The bigger square gearbox is what the crank connects to to raise and lower the landing jacks. The motor has wires connected by compression connectors. When you install the new motor there should be plenty of wire to make the new connection. You can use large wire nuts and tape them to keep them tight or use new compression connectors.
I talked to someone else that has replaced their motor and got a bigger motor. The one they sent me was smaller in diameter than the new replacement.
Below are a few pictures that may help you.