Well i managed to make it work again. I tried to reset the computer to a state, but it didn't work. In fact, i'm affraid that the problem come from my graphic card. Maybe it's damaged.
The reason why it stop working was because my computer decided to stop my graphic card, and with it the 3d acceleration. So I made a update of the pilot and it worked again, Achat could run.
But it's still very slow. I realized that the other programs i have who use the 3d acceleration are slow too. So it probably doesn't come directly from achat...