If you are seeing this in App Store,or when trying to download anything, it's most probably a billing issue, so you would need to contact Apple Care Support to have it fixed. Contact - Official Apple Support
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Try resetting the account's password (and then logging out and back in everywhere) : If your Apple ID has been locked - Apple Support
If that doesn't fix it contact iTunes Support and see if they can/will re-enable it : http://www.apple.com/support/itunes/ww or https://www.apple.com/emea/support/itunes/contact.html
There isn't a way of stopping an account from becoming disabled, somebody typing in the wrong password a number of times will disable it.
Your Apple ID has been disabled