how do i fix my phone that dosen't vibrate anymore?

Answer 1

didcha check under the settings??

Answer 2

Is vibration checked under Ring Modes? Failure to turn that on is the most likely cause.

If it is and you are not getting the vibration that part of the phone (a small motor with a wobbling rotating part) may have failed. Chances are (unless it is under a warranty) that no one will even try to fix it for you and that you could not get a replacement part and reinstall it.