Cameron's Closet (1989)

From IMDB: Tagline: A new place to look for terror. Plot Summary: A young and lonely boy named Cameron has telekenetic powers which his father experiments with. The young boy's loneliness is the cause of a strange spell to be cast. A demon from hell is unleashed and tries to take over the boy's soul. A delusional police officer and his new girlfriend psychiatrist are the only one's able to help the child after his father and mother's boyfriend are killed. The demon lives in the boy's closet and in a part of the mind that can only be reached by entering it. Click for poster: