The procedure has been met with significant criticism by many consumers, technical analysts and computer experts, who argue that it is poorly designed, highly inconvenient and ultimately does nothing to prevent software piracy.
When installing a retail copy of Windows or Office, the user is asked to input a unique product key supplied on a certificate of authenticity included with the program, which is later verified during activation.
Immediate activation is not required following installation, but the program must be activated within a specific period of time in order to continue to function properly.
Throughout this grace period, the user will be periodically reminded to activate the program, with warnings becoming more frequent over time.
It also points to this link for further information.However, there are different reasons that can cause the number not to work, as mentioned below.If you are installing Windows and the code you are entering is not working, make sure it is the correct code.There's a lot of confusion about CD or, more properly, "Product Keys", those long strings of numbers and letters you need to type in when you install Microsoft Windows.One source of confusion is where the CD Key comes from. The product key is typically printed on a label on the product packaging containing the CD when you purchase it.