Before you attempt to restore your iPad from iTunes make sure you have the latest version of iTunes and that you have backed up your iPad to iTunes or transfer and sync content to iClouds. Then follow these steps:
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Connect your iPad to your Computer.
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Select iPad in left hand navigation of iTunes under Devices.
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Choose Restore.
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When restore is complete, choose “Slide to set up”. You can then restore any information that you need to from the backup that you created before the restore process.
Resource: Apple Support