I have a RC 50, my experience is with this machine. I have realised that a lot of these machines are pretty similar, meaning i think this might help you. It can be either electrical or a hydraulic fault. First is to know if its an electrical issue(cheapest and easiest fix). I quick way to know if all electrical equipment is functioning as it should, is to go to the pilot control block. On my machine its to remove the centre bottom skid plate to get to it. My pilot valve has 4 electro magnet solenoids on it. 2 of these solenoids(single separately connected on the pilot valve) is safety engagement and the second DA hydraulics activation. Both energized on the same cable at the same time. Either put a test light or multi meter on the removed leads or remove the solenoids with cable and use a steel screw driver on the inside to see if they activate/magnetise. If you lower your in cab bar, door and seat switch (Safety devices) then they should magnetise or should energized those solenoids. If they do activate then you have no issues with an electrical fault. if they dont then its electrical from fuses relays door switch bar and seat switch in that order as possible faults. If the solenoids do activate then its a hydraulic issue. Start by removing the spool valves those 2 solenoids connect to on the pilot valve to see if they are free and working as they should. The spool valves get jammed easy with only slight contamination in the system. Either one of them jammed will stop the complete system as like in your case.