Could you post the errors you're seeing when you're trying to discover a Windows Server? Are you getting as far as seeing a missing credential error for example?, Does the Shazzam payload give you any indication of which protocols it finds open or gets refused connection attempts from? You will need at least TCP port 135 open, most likely 5985 and 5986, as well as the dynamic ports mentioned here.
For example, if you're seeing "Host is unreachable" errors, you've most likely not got a route to allow you to discover the device. Essentially, if you haven't already, request that the network teams open the default recommended ports before you start instead of trying to work out what might or might not be open.
