If you remember the email address that was used, you can try logging in on the forums with it (you don't need the username, just the password). If you can get in, then go to My Account at the top of the page, then to Stardock Account, and there you can change the email address on the account to a current one.

If you cannot get in no matter what you try, try contacting [email protected] with what details of the account you do remember, and they may be able to help recover it.