cause you F*^&*^* it somehow..... check all your wiring.. see if you accidentally disconnected a wire within the engine bay to one of the sensors or something..
I'd tend to go with this, but IIRC the car doesn't even run without the maf hooked up. takes a poop real quick.
Mine did the same thing. Unhook your battery for a few minutes to reset your ECU or go to Checker and read the specific code.