Happened to me too.
If you had backed up from your previous iPhone, it's likely to happen.
Solution:
1) You can do [home] button + [sleep] to reset; *but this is works temporary, but
2) "Reset All Settings" (the option that doesn't erase anything) should work perfectly.
**It will work, promise.***
For choice #2, however, you just have to go back to set {some} stuff you had set previously.