what to do if account gets blocked

Depending on why it's been disabled you might be able to re-enable it via this page : http://appleid.apple.com, then 'reset your password'

Or you might need to contact Apple : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page

If it then works on your computer's iTunes but not your phone then try logging out of your account on the phone by tapping on the id in Settings > Store and then log back in and see if that 'refreshes' the account on it