There are two places at least where ProductId gets stored. To see the first place, open Registry by going to START-RUN and entering REGEDIT and Navigate to [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion]. In right pane, look for key by the name “ProductId”. This is your Windows Product Id. Alternatively you can navigate to [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion] and still find same field with the name ProductId.