Tractor Repair: Case 1370 Powershift locked in reverse, clutch pedal, hydraulic problem

Question
When plowing with my Case 1370 I stopped at the end of a field, lifted the plow and shifted into reverse.  When I pushed in the clutch to shift the powershift lever into 1st I could not move the powershift lever, it was stuck in reverse.  At this point the tractor would not move either.  I am able to move the gear shift lever into any gear including park, however the tractor does not move.
Any thoughts on what the issue could be?
Thanks

Answer
 There is spool in the powershift control valve that prevents shifting into or out of reverse unless the clutch pedal is pushed if the engine is running.  If that spool sticks it would lock it in reverse, but if the tractor won't move, there has got to be something else wrong also.  Do all the other hydraulics work, steering, hitch, and remotes?  If not, there is another hydraulic problem that must be diagnosed first.  Can you move the powershift lever if the engine is not running?  If not, the problem is definitely in the control valve.