1. Try a Restart by pressing the sleep/lock button until you see the slider. Slide to power off. Restart by pressing the sleep/lock button until you see the Apple logo.
2. Try a Reset by pressing the home and sleep buttons until you see the Apple logo, ignoring the slider if it comes up. Takes about 5-15 secs of button holding and you won't lose any data or settings.
3. Remove apps from Recently Used list...
- From any Home Screen, double tap the home button to bring up the Recents List
- Swipe up on the app preview card to remove it from the list
- Press the home button when done.
4. If still a problem restore with your backup.
5. If still a problem restore as new, i.e. without your backup. See how it runs with nothing synced to it.
6. If still a problem, it's likely a hardware issue.