John Deere 410 dead hydraulics

I recently purchased a John Deere 410 I believe 1978 model. It had weak Hydraulics that eventually failed within the first few days. I was aware of this and planned for it. I put a rebuilt pump on it changed all the filters the fluid, and it worked beautifully. I used it two days later and discovered a leak so I shut it down,tightened the loose plug that was leaking, and noticed a good leak from a connection at the pump. I replaced the oring and ran it for two hours, all was well. I shut it down for about 45 minutes, and when I went to reuse it it started right up but had no Hydraulics no power steering won't move won't do anything completely dead boy I hope someone here can help and thank you in advance

John Deere 410 dead hydraulics