If it is the 3pt unit that is stuck up, as someone has mentioned, check the 3pt lowering speed unit. This is designed to let the fluid out of the cyl. It has a knob for adjusting, from fast to slow and to lock the 3pt in the up position. It should look like some springs pushing on a steel ball that closes off the fluid flow to the sump. It is possible that if left closed for a long time, it just might rust in place and jam the release. Thers are two relief valves in the 3pt also, the 3pt relief valve and the safety relief valve.
Another possibility is that the 3pt lever is not moving the 3pt valve.
If the system is stuck up, and the relief is relieving all the fluid going to the back, the fluid would get very hot. In neutral of course, the fluid flows thrugh the valve freely.