Tell the shop you have a bad disc? It is their problem, I have exchanged a few games like this before, Fallout 1&2 combo pack from ToysRUs, the first disc would not load on ANY computer I tried, and I purchased Street Fighter 3 EX for the PS2 and it was all scratched when I got it. They will exchange the game, if not. ***.

I would also try to start a new save, your save possibly become corrupt. Try that before going off on the shop.