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 .You'll be able to change the email address 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.