Hi 1stchevy,
You didn't mention what type of system you have, but let me assume the hydraulics pump also operates slide outs.
Two things have to happen to operate the hydraulic jacks or slide outs: 1) the pump has to run and 2) a valve has to open to allow fluid to flow to push/pull the rams/landing gear.
If the slide outs work, both of those things are working for the slide outs. If the landing jacks don't move while the pump works, the valve for the landing gear is not opening. It could be an electrical problem, or a valve problem. The first thing to check would be the switch wiring and the wiring to the valve.