Assuming your on the latest software release... If not, plug it into iTunes and let it update.
Sometimes they get a bit screwed up. So try the old re-boot option. Turn it off, fully, and turn it on again.
If that fails to improve, then try a reset. Hold the on/off button and the home button at the same time until you see the screen go blank and the apple logo appear. You wi,, not loose any data doing this.
... and if that fails, I hope a real techie reads this post and can help more than I can,