Well, you are able to log into this website, so thats a good start:

While logged into this website, all your registration information is available through the website, under the menu: 'My Account'/'Orders'.
Your registration number is there, as well as files you need to install.
Reinstall from the files provided, then enter the registration number that is available there.
If you are installing on Windows 7, there are special instructions in the Forums section.

For others that can't log into the site, I have some suggestions that may help you log in:
- if you remember your website password, and your old email address, you can log in using that old email address. Don't forget to update your user info after you log in.
- if you forget your website password, and your email address has NOT changed from before, click on 'acquire new password' under the login screen. This will help you log in.
- if you forget your website password, AND your email address HAS changed, please contact me by email and i will retrieve and update your account manually so you can log in.