1.How long haven't you watched TV?
或：How long have you not watched TV?
2.Why don't you do...是指“你（现在）为什么不（做某事）?”.
如：Why don't you watch TV?你（现在）为什么不看电视呢?
haven't you (done)...是指“你为什么一直都没有（做某事）?”,强调“到现在为止,一直都没有做”.
如：Why haven't you watched TV?你为什么一直都没有看电视?