I'm trying to find the title of an old movie - maybe 1980's. It is a sci-fi movie. A boys parents go away for the weekend and it is himself, his sister, and his friend. The friend is kind of a dork and listens to records with some sort of demon chanting on it. They find this rock or crystal in their back yard and then suddenly tons of little demons start running around taking over the house. In the end there is a giant monster and i think the boy kills it with some sort of firework or rocket. If anyone knows the title please let me know.
