Open Manage Network Manager communicates over a network. In fact, the machine where you install it must be connected to a network for the application to start successfully. Firewalls, or even SNMP management programs using the same port on the same machine where this software is installed can interfere with communication with your equipment.
Dealing with any network barriers to communicating with Open Manage Network Manager, any required initial device configuration to accept management, and managing security measures or firewalls--all are outside the scope of these instructions. Consult with your network administrator to ensure this software has access to the devices you want to manage with the Protocols described below.
One simple way to check connectivity from a Windows machine to a device is to open a command shell with Start > Run cmd. Then, type ping [device IP address] at the command line. If the device responds, it is connected to the network. If not, consult your network administrator to correct this. No useful information comes from disconnected or powered-down devices.