Does it have a lowering speed regulating valve down in front of the seat? If so could this be screwed all the way closed? On my Jinma, this will shutoff fluid to the 3PH lift cylinder(and send pressure to the half remote).
Are you trying to lift any load? Most control valves have some sort of safety relief to protect the structure if you bounce the tractor over rough terrain with a heavy impliment in the air. Could be this got activated by trying to lift too much, or a hard bounce, and never fully closed?
Not familliar with your machine. What kind of pump/s does it have? Any driven off the PTO that could have been disengaged? Just guessing without more info...