How do you enable apple ID

You might be able to re-enable it via this page : http://appleid.apple.com, then 'reset your password'

You might then need to log out of your account on your iPad by tapping on your id in Settings > Store (Settings > iTunes & App Stores on iOS 6) and then log back in so as to 'refresh' the account on it

If that doesn't fix it then you might need to contact iTunes Support : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page