Peugeot 307 sw hdi - Power Sterring stoping?

twice now my car's power sterring has felt like it had stopped, I re-started the car and it was okay. The next day the same thing has happened. I checked the power sterring fluid and this was very low well below the minimum line, I have now re-filled it. Would the low power sterring fluid cause this to happen or is there an another underline problem. It seems okay at the moment but its has only been a day since it happened.