There are three things to try: 1. Holding down the hold (top) and home (bottom) buttons at the same time for about 8-12 seconds. 2. Doing the same thing while the phone is being powered 3. Doing a restore through iTunes: http://support.apple.com/kb/ht1414 If your computer is not picking up the phone, try doing step 1 while it is plugged into the computer with iTunes open The first two will not delete anything. The third will if you have not done a back up recently. If you are on iOS 5 or later and have wifi at home, maybe you have been doing iCloud backups each night in which case you're in luck. Everything will come back to the phone.