I tried to install Audio Cleaning Lab 2016 on my new PC, but noticed I couldn´t find the serial number. Also the product was registrered with an email accont that is no longer active. What can I do to retrieve the serial number?
Your email address with Magix.com is your user name. It doesn't care whether or not the email account is still working. Just log in to your account, get your serial number, change your email address and your done. However, if you've forgotten your password, then that is another problem and you can't ask Magix to automatically reset it since Magix, like everyone else, sends a message to your email address for you to do that.
Otherwise, raise a ticket with Magix and tell them the problem.
Assuming you mean you need to raise a Support ticket because you cannot access your Magix account, please use the Support header found on any forum page and carefully follow through each succeeding page, always choosing the option to Ask Support.