This looks like the account was banned due to the recent gold seller hack wave.
Please first recover your E-mail and make sure it is secure. You will want to change the password on the E-mail account with the provider. Then please verify that your computer is free of malware. Finally, change the password on your account at our password change page, https://en.nostalrius.org/password.
Once all this is done, please get back to us in this thread.