there are 3 possiblities I can think of right off the top of my head:
1. You have the clutch lever pulled. the clutch must be engaged to in order for the kick starter to function.
2. Your clutch is not adjusted properly (too tight) and is not letting the clutch engage.
3. The last time the clutch was disassembled the inner hub was not aligned correctly.
Any one of these 3 will cause the kick starter not to function (the clutrch will just slip).