There are two small motors at each end of the slide which work together to move it. They are often hidden under the trim at the corners but take various methods to get to them. If one fails, gets unplugged, etc the slide doesn't move on that tend. Sometimes as simple as the link between motor and gear is all. Observe the track running along the slide on each end where the motor and gear move?
Parts catalog here:
click this snip to get better view!
They are on the same wiring circuit and should work together so if one moves it is not likely to be fuse, etc. Sorry!
If one can look from inside it is often possible to see the mmotor if we pull the rubber flap back. Not a big job to change but getting to it can be tricky. Several online videos may help.