Look to see if the emergency cable has been pulled. This is the wire with the hook that you attach to the hitch in case the trailer breaks free from the tow vehicle. Once the cable has been pulled you have to manually release it. I've accidently done this by pulling away from the trailer without remembering to unhook the cable. If you have a swig tongue and have used it lately you could have pinched the line which would cause a similar situation also.
From there based on you're stated maintenance of the trailer you're pretty much going to have to tear into the actuator to see why it's not moving. There's not much going on in there. A master cylinder and a shock absorber pretty much make up the entire assembly.