Power steering probs ?

Hi I have a 17 tdi 52 plate astra van put new battery on it and it was working fine for a month want out one day to start it and nothing!! So jump started it BUT no power steering. Arrrr.... So charged the battery started fine still no steering and battery light on in the dash!! A friend told me to turn the key on and off a faw times and boom power steering working and light want off on the dash mmmm.. but when I turn it off and back on it takes about 15 sec for the power steering to work????? Plz help..