Basically: In order to activate your software, you will need the serial number and a valid email address. Please note that as of 2014, you need to be connected to the Internet in order to activate the most current version of MAGIX software.

How to activate your software: You will automatically be asked to enter your serial number and email address after launching the installed program. Enter the serial number without dashes in the empty field. To register your product, enter your email address in the required field. Click on "Register and activate online now".

You may need to Ask Support and explain the trouble you are having. See also item 6 here for registration help.