I can't hook up the battery because the neg. cable is sparking, why?

I bought a new battery and had the auto store put it in. The guy put it in backwards and it started smoking. He then relized the battery was backwards and turned it around. But now you can't hook up the battery because it is sparking. I thought it was the altenator and unplugged it. Also hooked up a test light and pulled every fuse in the car, test light will not go off. Do i have an electrical short or what and how can I fix it? I have great hopes of restoring this car. Any help would be greatly appreciated. Thanks