The Basic Troubleshooting Steps are:
Restart... Reset... Restore from Backup... Restore as New..
Restart... Reset > http://support.apple.com/kb/ht1430
Restore from Backup... Restore as New > http://support.apple.com/kb/HT1414
If you try all these steps and you still have issues... Then a Visit to an Apple Store or AASP (Authorized Apple Service Provider) is the Next Step...
Be sure to make an appointment first...