Ford 3910, John Deere 420C, Kubota G32XKS, IH 2606, Bad Boy Maverick-60"
Welcome to the Forum!
I'm not familiar with your tractor but many "Live" PTO tractors require the clutch to be depressed halfway to engage. Or, Perhaps the clutch disk(s) are stuck together from not being used.
What specifically happens when you try to engage PTO with engine running? If you get grinding follow Tinhack's post. What happens if you engage PTO with engine off then start engine? Does PTO remain engaged or drop out? A better explanation on symptoms could lead to better suggestions for a solution.