1. Go back to the home page of the forum, and click on "Log on".
2. Click on "Resend activation email".
3. Enter the username and email address that you used to create the account.
4. You should then receive the activation email. Complete the activation as normal, and your account will be active.
5. Log in on forum and in-game.
If you're having any issues trying to log in or getting your game to work, check this FAQ thread.
Have fun!