Have you tried a reset?
Reset: Hold the Sleep/Wake and Home buttons and don’t let go until the screen goes dark and the Apple logo appears (no data will be lost)
Reset All Settings:
Settings > General > Reset > Reset All Settings
You will not lose any data but it will reset the settings in your Settings app.
As a last resort, backup, connect to iTunes and restore (http://support.apple.com/kb/HT1414).
This will redownload and clean install iOS 7.
After it finishes, go through the setup and restore from the backup when prompted.