Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_2_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5H11 Safari/525.20)
Try a hard reset. (hold the home button and the on/off button until the Apple logo appears)
If that doesn't work you'll have to do a restore of the software using iTunes. You should be able to restore it from a backup and be fine.
Then did you go into settings, chose sounds and make sure Vibrate is set to on? Then move the silent/ringer switch and feel it vibrate? If that doesn't work, go to an Apple Store.