Here is procedure to activate Norton Internet Security
Make sure that your computer is connected to the Internet.
Launch Norton Internet Security via your desktop icon or the Start Menu (All Programs > Norton Internet Security folder) If Norton Internet Security doesn't appear in the Start Menu, it means the software was removed.
3.It is recommended to create a Norton Account in order to manage your Norton products, get the latest product updates and access special offers.
Enter your email address.
If you already have a Norton Account tied to this email address, you will be asked to enter your password
If this is the first time you create Norton Account, you will be asked to enter some personal information.
Your Norton Account has been created. The next steps will guide you through the process to activate your full year product.
On the bottom-right corner of the Norton product window, click Subscribe.
Type in your Product Key.
The Product Key is a unique 25-character alpha numeric key which was sent to you in the order confirmation email you received.
Click on the triangle next to the product key field.
You're done! Your full product is now activated.
You can get more help from here
Hope this helps, if so do rate the solution