yes, systematic diagnostics.
now, back to larry's first question.. do you have any sort of diverter or remote valve fed off the top cover of your hyds cover. including power beyond 'sandwich' plates.
if not, then time to see if you have oil at the pump head by removing the plug in the top/front of the pump with engine off and run her over / crank.. if oil comes out.. stop.. put plug in, then remove plug under seat in 3x5 option cover and do same test.
if oil there.. then stop, plump in a 3000 psi gauge into that hole.. chain a lift arm tothe axle, and start tractor and run 3pt lever up ( if you have remotes you can also pressurize a remote with a hyd gauge in the lift port.. etc..
post back what she makes.
at this same time I'd hav ethe fill plug out and using a strong led flashlight and a mirror , look in to see massive oil spray / squirting going on from anywhere inthe top side.... especially if the psi made on the gauge is lower than 2100 psi..
also note if running the lift up whiule chained labors the engine any.
ps.. if it has a proofmeter.. is it working?