2003 Nissan Sentra fuel system problem

My wifes check engine light came on the other day. We too it to a repair facility the code was PO462 or fuel level sensor. I tried to reset the sensor and messed up her car. There is a black box underneath the rear of her car, it says purge, fuel tank. It lines ran to it along with two electric plugs. I unplugged the one above the word puge. I then plugged it back in. The car started fine the light still appeared but now when we press the gas it has no power. Can you tell me what I may have messed up. I have tried replugging it back in several times. Im not even sure what the black box is called. I would appreciate any help[ you could offer.