Is your haptic feedback working? If that works then your vibration mechanism works.If not then it would indicate hardware issue. If it works, have you checked in settings >sound>vibrate and make sure It isn't set to never or only in silent mode? Lastly there is also a vibration test that you can perform by entering a code on the dialer. (you can Google galaxy s vibration test pattern as I don't remember what it is) but I have no clue if that could potentially brick your phone if not performed properly,so do so at your own risk. If none of this works then like said above,bad unit....return it.