We will try to help, but will need more information about when it did work, what has seemed to happen since it worked, and what "doesn't work" means.. Oil and filter change history will help too. Take us through what is happening..
Does the power steering and SCV operate ?
Is the shaft on the front hydraulic pump spinning or slipping on the drive collar? Oil level? Transmission oil filtet and oil screen?
Free JD parts book. John Deere - Parts Catalog
Have you attempted to change setting on L/D lever under seat. Does this tractor have a frt end loader? If so how is loader controlled(scv or ind valve)?