you may want to dissassemble the laptop again and check to make sure you didn't inadvertantly ground anything out after you reassembled it.
i hate to say but it sounds like you really may have cooked the laptop. if it's an HP or a compaq, which are notorious for those kind of power plug issues, you may have to kiss it goodby, though check to see if any warrenty may be left on it. just don't let them know what you did!