WMI get all users state

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WMI

Hi,
I'm trying to get all the users state or status, not sure what is the property name.
I found this code for the userName property:

ConnectionOptions options = new ConnectionOptions();
                options.EnablePrivileges = true;
                ManagementScope scope = new ManagementScope("\\\\" + fqdn + "\\root\\CIMV2", options);
                scope.Connect();

                SelectQuery query = new SelectQuery("Win32_ComputerSystem");
                ManagementObjectSearcher searcher =
                    new ManagementObjectSearcher(scope, query);
                string machineUser = "";
                foreach (ManagementObject os in searcher.Get())
                {
                    machineUser +=" "+ os.GetPropertyValue("username").ToString();
                }

I would like to also have the user state, if the user is on sleep, inactive, active etc.
Where can I find it?
Thanks in advance :-)


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one more thing, when no user is logged on

os.GetPropertyValue("username").ToString();

throws an exception.
Is that the expected behavior? How can I tell if that's the reason or it's something else?
If I could just have the users and their status, that would have been great :-)