Fordson 1962 Hydraulic?

My 1962 fordson hydraulics have just stoped working after been stood for five weeks, this as hapond in the past but after a while they start & work ok, this time they will not kick in, why. Had the sump pick up wire mesh off cleaned it, have taken some of the valves out at the top near the auxiliary valve (pump pressure relief valve) run the back end but very low flow of oil no presure. Have known people say about this before, his it something common to them or just the pump gone. got a manual and a workshop so can do the job but if you know of this type of problem could save me time. regards robin.