Q: How can I enable my iTunes Store account ?

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 > iTunes & App Stores 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