I don't know if there's much that can motivate someone to learn the guitar if they don't want to. But here are some suggestions: be strict with yourself... become passionate about learning the guitar. Forget the TV and homework, just play play play. Also, if you got a teacher, he might be able to provide the structure you may need in order to concentrate and learn. For me, there's no better motivater then hearing an awesome guitar peice, it gives me a need to learn how to play it.