I have a 1998 john Deere 870 compact tractor. I changed the hydraulic fluid in the tractor and replaced the hydraulic filter. After having changed the hydraulic oil I last the ability to steer the tractor. The steering wheel turns but there is no movement in the steering arm or tires. I don't know if it was a coincidence that I lost steering when the oil was changed or something happened in the process. Any suggestions as to where to start looking? Thank you.