Reset your device: press and hold Home and Power button until the Apple logo appears. Release both and let the iPad power up. This won't delete data or settings.
If it doesn't solve your problem, go to Settings - General – Reset - Reset all Settings. You'll have to go through your settings again afterwards and select what you prefer.
The next solution would be to restore your iPad using iTunes on your computer. Here's what you have to to: http://support.apple.com/kb/ht1414