My JCB has hydrostatic steering (seems yours is the same) powered by a seperate pump to the main hydraulic pump, driven off the engine timing gears.
Failure of steering pump will not affect loader/backhoe operation.
Assuming king pins aren't siezed, check that steering pump is providing pressure to the steering ram, and that the pump is being driven.
If you should happen to have a Leyland engine the pump is driven off the timing gears via an idler gear whose bearings tend to break up, possibly causing disengagement of gears if left too long.
If any of the above fits your m/c, post query again and I MAY be able to help further.
Mr. Toad, August 2008