No trailer power when connected to the truck hitch. Why?

Did you have the truck running when you tried to use the jack and slide? Many trucks have the power line to the camper tied into the ignition. If the truck is off the power line is not live. This is to prevent the camper from draining your starting battery over night.

If that is not it follow the power line from where it plugs into the truck to the frame of the camper. Its probably connected to an inline breaker attached tot the frame under the camper. Push the little button on this breaker to see if it is tripped.