Before asking for a new activation code to be sent, please check your Junk/Spam folder.
If you haven't received your activation code and you still have the registration window open, on the page where you need to enter the activation code
you will need to check the email address shown and you'll be able to change it and request a new activation code to be sent.
If you haven't received your activation email and you've closed the register window, you need to restart the My Account registration process.