To de-register the installation, using your web browser, browse to magix.com and click the Account login icon top right of the homepage and login using the email address and password used to register the program if you no longer have that email address you can still login with it.
Select My Products you should now see your registered product with a download link, serial number, and under the Show more details link the registered installations - here you can de-register the crashed computer.
After de-registering if you have a new email address - you can also change this under User Data, Change Details.