What brand of hydraulic system do you have? If it's HWH, there could be a ground problem. Everything seems to be in order but when you try to drop the jacks or extend the slides, nothing works. Lights don't even dim on the control. And you can't hear the motor running, in most cases.
Up until '04, you'd likely find Winnie did use HWH and the hydraulic manifold was usually under the living room slide. After '04 you'd find the manifold under the stairs. Follow the motor noise to find yours. When working on that manifold with all the wires, tank, and the hydraulic solenoids, note that you can't see the ground wires. Those are underneath the manifold where you can't see them, all the wires have ring terminals and they're all attached to a bolt welded onto the frame/chassis. That assembly often rusts and corrodes so the system won't run. Quick test is to reach under there with a rubber mallet and whack them and see if the system comes back on.
Here's what mine looks like, followed by the stud where all the grounds are connected. As I said, it's underneath, have to crawl under to work on it...
When my system had intermittent problems, I localized it to that ground stud, but it snapped off when I tried to remove the bolt. So drilled new holes, cleaned all the ring terminals, than reattached them to two new SS screws I'd threaded into the frame.
One other problem of note to that sort of setup is the big 40 amp inline fuse HWH required very near the manifold. Those can corrode out too so check that while you're under there.
If you have a different style setup, maybe post a picture?