The Invisible (2002)

Nicklas lives a pretty normal teenage life, until one day, not far from graduation, when a gangster from his school beats him up. Nicklas passes out, and the next day when he returns to school he notices that nobody seems to notice him. As he tries to get attention he notices that his actions disappear the moment he has done them. He throws a book and as soon as it lands it's back where he picked it up. He has returned as a ghost, but he can do nothing but passively observe as the police stand clueless to the murder.