you cannot login because your account has been locked.

If you haven't already done so then you will need to contact iTunes Support as the message says (these are user-to-user forums) and see if they can re-enable it (or tell you if your account can't be unlocked) :

- go to http://www.apple.com/support/itunes/ww

- select the flag of the country where you are, and which you have on your iTunes account

- scroll down to the bottom left of the next screen and click on Contact Support