gradually die or all at once?
where to start?
1, check hydro oil at the dipstick.
if it has oil, then check to see if it will lift with no load.
if it will not lift with no load, check pump for prime at the top/front plug on the head.
if it has oil there, check under the seat on the option panel, with the plug in it.. check for oil there. ( if you have a remote there.. check to make sure you didn't kick it engaged ) if not engaged.. check to see if remotes work. if they do.. pump and relief are fine..
if oil there under the seat and no remotes, then pull cap on rear and look in for massive leaks from top.
if nothing apparrent... pull top cover for a looksee.
no sweat on the diagram.. your service and parts manual have them.
( what? no manual? shame on you! )
get one at the CNh parts site... free..e tc..