Hard reset your phone to factory default setting you will lose all of your sms and apps,so you must back up your apps and sms.
1. Go to home screen, press menu button.
2. Choose the Privacy
3. Press Factory data reset.
4. Read the disclaimer, then Press Reset.
5. Last,press Erase everything.
6. Restart , you will see the phone as a brand new phone.
If that doesn’t work,hope this video can help you: