What could be wrong with my 23 month old son?

I can think of only 7 words he can say, he hits his head on stuff a lot, and he does stuff he KNOWS he's not allowed to do. He says only the basics. He pounds his head on the coffee table, the TV, the floor, the wall, anything he can find. He has ended up with bruises and cuts from it. He will climb anything he can find to mess with his TV and DVD player, yet as soon as he hears me he runs, he will get into the movies and peek back at me and smiles evilly, and he is just always misbehaving!! I have tried getting him to speak but he refuses, I have tried ignoring him hitting his head, it does nothing, and I have tried him when he misbehaves and it doesn't phase him, I can't put him on timeout cuz his room doesn't have a door and he spends most of his time in there anyway just playing in his room alone. I am really worried. What could be wrong and what should I do?!?