You have a period of 30 days to activate your Windows license (official). Beyond that, you can not use this system and you can not activate Windows.
Two solutions come to you:
activation by phone.
In both cases, Windows will ask you to activate your license until it is done.
This is the easiest method.
Choose method By Internet
Follow the instructions. The system checks the validity of your license number and, if it is not considered a pirated license, your license is activated automatically.
Activation by phone
You can use this method in the following situations:
for those who have no internet connection.
for those who encounter a problem trying to activate over the internet (a configuration change or too many relocations),
for those who have waited too long to activate Windows!
Warning! Preferably use a phone and not mobile!
Choose method By phone
Choose your country, which will allow you to specify the number to call,
Dial the phone number,
In the dialog, you have a number of the license, grouped of digits (3 items), you must input them via telephone keypad,
The system checks the validity of your license from the input that you just made,
If all of the information are entered correctly and validate, your license will be activated.
Note that this procedure:
allows you to re-enter the code, in case of input error,
listen to each ID number entered.
To do this, listen carefully to the initial message telling you which key to use on the telephone keypad in case of error.
If the activation system rejects your application, this means that:
Either you have entered the wrong combination,
Either way, your license is considered invalid, pirated.
The activation process
Via the GUI
Click on Activating Windows
By command line:
Licence deemed as pirated
If the activation system refuses your license, and you're are certain that no mistake were made (in the case of activation by phone):
Contact your reseller and ask for your original Windows or at worst ask for a refund.
You can contact Microsoft if you are uncertain about what should be your next move.
The number of machine on which a licenses is valid
As a reminder, and despite of many assertions, you can use your license number on a single machine at a time.
Suppose you have already activated your license on a machine A, it allows you to benefit from the new updates. Considering that you assemble a new machine B and just to save some money, you make use of the samelicense as the machine A.
You may be able to register new machine B. With some luck!
But the fact you can update the machine B, will now make it impossible to make any updates on the machine A, which will be then considered as a machine running an hacked version Windows.
The choices are:
Either buy a Windows license,
Either install a free operating system such as GNU/Linux, or BSD.