First, would you go to
http://microsoft.com/genuine and click the Validate Windows button.
If it Validates as Non-Genuine please post here th exact information that page provides. (including error messages, directions to fix the issue and so on)
If the Online Validation does not resolve the issue, please try the below steps:
1) Click Start button.
2) Type: CMD.exe into the 'Search programs and files' field
3) Right-Click on CMD.exe and select 'Run as Administrator'
4) Type:
net stop sppsvc (It may ask you if you are sure, select yes)
Note: the Software Protection servive may not be running, this is ok.
5) Type:
cd %windir%\ServiceProfiles\NetworkService\AppData\Roaming\Microsoft\SoftwareProtectionPlatform
6) Type:
rename tokens.dat tokens.bar
7) Type:
cd %windir%\system32
8) Type:
net start sppsvc
9) Type:
slui.exe
10) After a couple of seconds Windows Activation dialog will appear. You may be asked to re-activate and/or re-enter your product key or Activation may occur automatically. (If you need to reactivate, please do so by Phone).