When a Norton product is installed on your computer, you have to enter a product key (sometimes referred to as a PIN number) in order to take full advantage of the software's capabilities. If you need to find this PIN number at a later time, you can do so by searching in the files of the program.
Open a Windows Explorer by right-clicking on the "Start" button and selecting "Explore" (in XP) or selecting "Open Windows Explorer" (in Vista/7).
Browse to the "C:\Windows\Documents and Settings\User_Name\My Documents\Symantec" folder, where "User_Name" is the username of your account.
Double-click on the file that ends in "?key.txt." This file contains the PIN key for your Norton product.