Q: how can i acitvate my account

If you mean that it's disabled then 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 phone by tapping on your id in Settings > iTunes & App Store 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