first... a serial number of unit might help get the right service manual. But with that said you need to get a 3000psi hydraulic test guage.
Look on the hydraulic manifold block, it should have a quick disconnect test port to connect a guage to. Also locate the system pressure relief valve at R1 on manifold.
Now with guage in place, press and hold right steer and let system stall out, take a reading on guage and then release steer button. The pressure should read the rated relief pressure for this unit which should be around 2150 psi. If you do not get this pressure reading try and adjust pressure on relief valve to get this pressure reading.
If you DO have correct reading then i would start looking for a bad steer control valve or a bad cylinder, worn packing causing a bypass in cylinder might be your problem or possibly a faulty steering valve in manifold block.

I'm basing my information on older machines ( i used the oldest serial number range in skyjacks manual list ) Newer machines may be different. You can go to skyjack. com and find your manual as well, they are open to the public ;o)

So whats that serial number?