Here's a primer on remote WMI:
https://msdn.microsoft.com/en-us/library/aa389290.aspx
In our environment, we basically run winrm quickconfig on all our machines, for those not joined to a domain we also add them to the TrustedHosts list. For machines not joined to a domain, there's an added difficulty if you are using the IP address instead of the Host name, it definitely offers a few challenges.
A good strategy is to get remoteWMI to work, then we integrate it in RDM. We like to use WMIC.
https://msdn.microsoft.com/en-us/library/aa394531(v=vs.85).aspx
This is a lot of information to go over, please contact us at ticket@devolutions.net if you hit a hurdle.
Ensure the user account has the necessary permissions to access a computer remotely Securing a Remote WMI Connection (Windows).
You can also find troubleshoot tips in WMI Troubleshooting (Windows).
Invalid Class WMI or WMI class not found on Windows Server 2003. On Windows Server 2003, Win32_Product is not enabled by default. You can enable it by following the steps provided in the link below:
The WMIC command is used to test if you have access to the machine through WMI. You need to enter the following command below;
wmic /NODE:"ComputerName" bios get serialnumber
Below, an example with other credentials;
wmic /NODE:"ComputerName" /user:"username" /password:"password" bios get serialnumber