sounds like your inline fuse is blown or someone took it.
There should be a 30amp fuse holder in the line for jack. Check along the wire running from battery to jack. OR you left lights on, radio on, etc. in trailer and it drained the battery.
DO you have power for lights in unit. if so then it's got to be a fuse in jack.
May have to use manual crank on top of jack to raise, lower it.
I always disconnect power when in storage, as lp detector and other thing like fridge controls, etc, draw power with battery hooked up.
Good luck finding the problem. it should be a easy fix for future references