Our 4250 powershift sheared all the bolts on the front clutch pack once so it wouldn't do anything. In that case though it fell down and the motor couldn't even turn over. Was odd though, it must have done it while running but stayed together until shut off. Then would not turn over.
You might check the pressure lines running into the side of the trans on the right side too. Can't remember which.
One thing is to see if the forward, neutral, reverser lever moves all the way to reverse that is on the right side in front of the back tire on the transmission housing, you should have somebody in the cab to move the lever to see it moves from neutral, forward and reverser. You will have to take the ball joint off and see if it is reverse. This lever is the smaller one. Make sure the ball joint is good, no play.