I take it you mean the garage replaced the belt and the pump? Its likely the belt snapped because the old pump siezed, as modern belts dont usually just snap, if the pump failed internally its possible swarf or little bits of broken pump has got into the system causing a blockage, anything from a total block to a restriction. I would get it back to the garage as if you ask me, they havnt fixed the problem. Is there any effect from the P/S ? Or is it totally innop?