Try these steps, in order.  If one doesn't fix the problem, go on to
the next one:

1. Someone might have hidden Network Neighborhood using Tweak UI.  Go
to Control Panel.  If Tweak UI is present, double click it.  On the
Desktop tab, put a check mark in the Network Neighborhood box, click
Apply and OK.

2. Go to Control Panel | Network.  Remove Client for Microsoft
Networks if it's present.  Then add Client for Microsoft Networks.
Reboot.

3. There could be a system policy hiding Network Neighborhood.  Run
the registry editor, open this key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer

Delete the value named "NoNetHood".  Reboot.