[Motor31]

It is impossible to diagnose this without all the info. In this post you indicate it's a hydraulic system. That is new information you left out earlier.

What brand and model trailer do you have?

Is the hydraulic fluid topped off?

What happens when you push the button on the inoperative slide? Does the pump run at all? If it does run, does the pump sound like there is a load on the pump or is it free spinning with no load. In other words does the pump sound different on the 2 inoperative rooms than the functional one?

Have you checked the hydraulic manifold, hoses and rams for leaks?

If you have a mobile suites trailer, there are knurled knobs on the hydraulic manifold. All of the knob should be turned counter clockwise as far as they will go.