Try logging in to your account at magix.com, using the email address and password used to register MEP 2016.
Under My products you should see you registered software with installer download, link, serial number and under Show more details, your registered installation(s) - deactivate the computer registration and then try registering it again in the program, do also check that your Antivirus/Firewall is not blocking the program from the Internet.
If you get any error messages please post a screen shot of them.