Message THIS COPY OF WINDOWS IN NOT ACTIVATED but no activation wizard

One of our Lenovo computers (PC has been in used for couple of years) started showing the message that "this copy of windows is not activated, in order to be properly licensed this copy must be activated" but I don't have the activate windows option in system tools and can't run the command to start the activation wizard.  Tried calling support and after I explained all this to several people the last person to take my call forwarded me to the activation line wich I could not use sinceI can't run the activation wizard.  I tried a tool to re-enter the product key in case this was the problem but the key was the same that was already registered.  Don't know what else to do.