I agree with Iggy in his attempt to help.
Questions I have........
You list your rig as 2015 GT 378XL.
Is this your first time using the rig?
Did you get any introduction/training during your initial acceptance of the RV?
After deploying the leveling jacks, (then turning off the engine) did you connect your power cord to AC power, or start your generator to take the load off the batteries to deploy the slides?
Remember, you need the engine running with parking brake engaged to deploy/retract the jacks. Engine must be off to deploy/retract the slides. AC power from your house or the generator is suggested for slides to be deployed/retracted.
I'm guessing the breaker under the steps has tripped causing nothing to work anymore. Iggy has pictures of this breaker.
Ken and Terry
2010 Georgetown 330TS being pushed by our
2017 GMC Terrain toad (4 wheels down)