If the motor runs, and it is a Lippert slide, more than likely the stupid plastic gear that moves the slide is broken. Ours was on a bedroom slide, and the mechanism is under the floor of the bed structure. The underbed storage had a plywood floor that came out with 6 screws, and there was the broken gear, in plain site.
If you can find the machinery, you can unhook the gear rail and push the slide in by hand.
If it is an older slide, Lippert does not make any parts, and aftermarket gears are not available. My gear was built by a local machine shop, using the old plastic one as a model.
good luck.