6718 hydraulics

i've got an old 6718 and hydraulics were working okay (ish - a bit sticky engaging the lever on floor by left foot) - havent used it in some time and now while the front arms are up there are no hydraulic controls at all - other than lowering the arms (which i obs dont want to do)
Any ideas where to start ?
complete novice when it comes to tractor mechanics BTW

When you say front arms I presume you mean front loader? does it lift real slowly even with revs?. If the loader is up but the back arms won't lift you might need oil in the back end.