And if that does not work power it off and on. Hold down the power button until the red slider shows, slide it. Wait a few seconds after it's completely off, then press the power button for about 3 seconds to turn it back on.
And if that does not work, do a soft reset.
Hold down the power and home button until the apple logo appears; 10 to 15 seconds. Wait for it to finish rebooting. It will take a few minutes.
If that does not work, call Apple tech support.