Ken and Terry were correct that you should turn off the leveling system when you are moving. I assume that your engine was running and your parking brake engaged when you tried to lower the jacks. Have you checked the reservoir and the hoses? Is there fluid? The Georgetowns have had a problem with the orange hoses blistering. Does the pump motor run? As for the slides, the slides on the 280DS are electric and not associated with the jacks or the hydraulic pump.
Gary Shapiro, 2011 Georgetown 29' Class A
Dash, Molly & Lily - now at the Bridge and forever in my heart
Shadow - 4-year-old Greyhound
Hannah - 1 1/2-year-old GSD rescue