People have had luck with:
Re-boot ipad.
Press and hold the Sleep/Wake button until a red slider appears, then drag the slider. Then press and hold the Sleep/Wake button until the Apple logo appears. page 128 iPad user manual.
force power down if the above give you trouble.
Hold down both the Sleep/Wake button and the Home button. Ten seconds or more. Hold until the Apple logo appears.
more details on re-booting:
http://ipad.about.com/od/iPad_Guide/ss/How-To-Reboot-Your-iPad-Power-Off.htm
Restore to factory settings by loading the latest version of ios that your machine will support:
Do a full backup of your device. Twice is best -- cloud and computer.
"You can use iTunes to restore your iPhone, iPad, or iPod touch to factory settings and the latest version of iOS."
http://support.apple.com/kb/HT1414?viewlocale=en_US&locale=en_US
"You can put your iOS device into recovery mode, then restore it using iTunes.:
http://support.apple.com/en-us/HT201263
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You need to backup to the cloud or to a computer. You need to sign out of the account on the ipad. You need to do the following:
What to do before selling or giving away your iPhone, iPad, or iPod touch
http://support.apple.com/kb/ht5661
Here is some further info.
-- Learn what to do if your iOS device is lost or stolen.
-- Learn about Find My iPhone Activation Lock.
-- If you registered your device with Apple, you can unregister it at My Support Profile.