What kind of system, Hwh or powergear? Be sure your batteries are fully charged and run the engine when using slide. Check for obstructions, good ground at hydraulic pump, read the manual before doing anything.
If still no success as said before call the Mfg. They are both very helpful.
Retired RV Technician
Travlin the West
Winnebago Outlook, Victory Vision, Silverado 3500, Dog ,Wife ( not in that order)