what happens when you receive your activation key via email? and you dont know you will need it a year later to activate it but the email is long been deleted.
It is your responsibility to keep a record of your serial key! Sorry, but that needs to be said first.
However, assuming you registered your software when you installed it originally, if you go to this page and log in to your account you will then be given an option to view "My products" where you will find your key.
OTOH, re-reading your post, I wonder whether you actually mean you bought the software a year ago and are only now just attempting to install and activate it? In which case, you will need to use the Contact button in the footer of every forum page to contact Sales and ask their advice. At the very least I suspect you will need to provide proof of your original purchase.