You email address is a user name. Why not just activate using the old email address?
Secondly, you can update your email address in your account with Magix.com. Then try again.
If you have forgotten your password for your Magix.com account and no longer have access to your old email address, then you won't be able to use the 'forgot password' feature that almost every site has. That can have far-reaching consequences if you have not updated all of the sites that you use, like your credit cards, banks, etc. Magix is just one of them.