1999 Vauxhall Astra power stearing not working all the time when cranking over car

have you checked the power steering fuse and the main earth wire to battery terminal,check for live from fusebox

" power stearing not working all the time when cranking over car " Do you mean the power steering is not working when you are starting car ? Is it ok when started ?

no not all the time and ye have checked all fuses

could it be the ignition switch

Have you tested your battery and the alternator output ? because if the battery voltage falls below a certain level, the EHPS system will shut down.

if thats the case why does it work if you turn it on and off sometimes but not all the time

this is normal it because the battery does not have enough charge when you are cranking it over and the pas ecu goes 'fuck it no power i going to turn my self off'!!! leave it a min when you have started the engine and then move the car and it should work then cause it needs a pick up off the speed sensor to kick the pas ecu's arse to make it work!!!!!!!!!!! hope this is helpful