The line between teen angst and demonic possession gets even blurrier in The Haunting of Molly Hartley, a lightweight horror pic about a troubled 17-year-old (Haley Bennett) who tries to escape her spooky past by enrolling at a posh prep school. Soon enough, homework gets neglected as she’s plagued by headaches and creepy visions — not to mention lame pick-up lines from the resident pretty boy (Chace Crawford, looking like he got lost on his way to the Gossip Girl set). The story’s a snooze, so the filmmakers punch it up with smash cuts and thunderclaps that turn the most laughably banal items — birds, mail, an alarm clock — into cheap jack-in-the-box shocks. They’ll make you flinch — but then again, so will most of the dialogue. C?