There are a few things you can do to try and remedy this in a basic way...
- Try a hard restart (holding power and home button together to restart the device)
- Try resetting your network settings (remember to have any wireless network passwords ready to reenter because this will essentially eliminate those saved networks)
- Go into your settings and sign out and then back into your Apple ID...sometimes it can get hung up for whatever reason, this will usually kick it back into gear
Ultimately...if nothing really seems to do the trick, you can backup the device and restore it in iTunes.