Can’t See Some Computers on Network Map
When browsing the network map in Windows 7 or Vista, you may be able to see some computers, but not all of them. This is because network mapping is not enabled on domain networks by default. You may see this screen on a client machine:
“Network mapping is disabled by default on domain networks”
To enable, go to a domain controller and enable the policies in the image below through the domain default policy editor: