If for some reason your Windows 7 or Windows 8 online activation fails completely, you may see an Activate by Telephone option in the wizard. You can always use this option to activate your Windows 7 copy.
In case a connection to the Internet is not available or if you get any of the following messages, in spite of having a genuine key, phone activation is then the best choice:
The Windows 7 product key you typed is invalid for activation
The Product key you typed cannot be used to activate Windows on this computer
Windows 7 has many license states; from Licensed to Unlicensed and many in between:
Licensed: You see this status after a successful activation.
Initial Grace Period: This is the state after you have installed Windows 7, but have not activated it. You will be reminded to activate or Windows will attempt to activate it online automatically.
Additional Grace Period: If major hardware changes are made to your computer, Windows may prompt you to reactivate Windows.
Notification Period: Once the grace period expires, you will see message that Activation is required.
Non-Genuine Grace Period: You may see this after Windows Genuine Advantage has determined that your Windows copy is not genuine.
Unlicensed: This appears for unlicensed copies.
Open C:\Windows\System32\slmgr\ and right click slmgr and open with Notepad.
Here, you can see many license states and what to do if you get these messages. Of course, the relevant messages are always displayed during Activation, but here you will be able to see all of the Windows 7 Activation states.
For example: L_MsgErrorText_11=”The machine is running within the non-genuine grace period. Run ‘slui.exe’ to go online and make the machine genuine.”
If inspite of having a genuine Windows 7 license, you are having problems activating your copy, use this command (As an Admin) to reinstall license file:
cscript slmgr.vbs -rilc
At the end you should be able to see a message:
License files re-installed successfully.
Go here to see how to rebuild the Tokens.dat file in Windows.
Also read : The Windows 7 Activation FAQ