If you are talking about the large room slide with under floor rails it may be that you have broken a shear pin on the drive to the non-motor side. You may have to push the button for extend while someone else pushes on the right side to get it out far enough to check the shear pin. If you are talking about the LCI Schwintek then it may be a loose connection to the motor on the side not working or a bad motor.
Jake my sidekick (yellow Lab)
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho