Try a restart, and if that does not work a reset.
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears. Apple recommends you restart the iPad at least once a month.
and then a reset if that does not work.
Reset: Hold down the power and home buttons until the Apple logo appears. The iPad will reboot. This usually takes a bit longer than a restart. takes a bit longer than a restart.
Finally, if none of those work go to Settings > General > Reset: Reset All Settings. This will not erase content, apps, or accounts; but you will have to re-tweak most other settings when done. Be careful to tap the right button.