Reset your device: hold down the home button along with the sleep/wake button until the screen goes black and you see the Apple, then let go. (No data loss)
If this doesn't work, backup and restore your software via iTunes. If the problem continues, restore as a NEW device. If this solves it, that means there is some corruption in your backup file, or maybe it's one of your apps causing the trouble. If the problem is still there, you should take it to the Genius Bar at an Apple Store for evaluation.