[meccadon123]

Dropping it or taking the cover off/putting it on can affect the vibration. I actually had this problem before and adjusting the battery (out/in several times)tapping on the vibration mechanism,actually tapping the corner of the bottom can sometimes jar it back into place(the vibration mech.) If you press on the back cover to hard it will mess up the vibration mech. . I know this sounds a little odd, but trust me, i got mine working this way after it stopped.