Add windows Host to Nagios server

# vi /usr/local/nagios/etc/nagios.cfg

here uncommand the configed windows file

# Definitions for monitoring the local (Linux) host
cfg_file=/usr/local/nagios/etc/objects/localhost.cfg

# Definitions for monitoring a Windows machine
cfg_file=/usr/local/nagios/etc/objects/windows.cfg

# Definitions for monitoring a router/switch
#cfg_file=/usr/local/nagios/etc/objects/switch.cfg

[root@ADV-CACTISERVER objects]# /usr/local/nagios/bin/nagios -v /usr/local/nagio

Nagios Core 4.2.0
Copyright (c) 2009-present Nagios Core Development Team and Community Contributo
Copyright (c) 1999-2009 Ethan Galstad
Last Modified: 08-01-2016
License: GPL

Website: https://www.nagios.org
Reading configuration data...
   Read main config file okay...
   Read object config files okay...

Running pre-flight check on configuration data...

Checking objects...
        Checked 15 services.
        Checked 2 hosts.
        Checked 2 host groups.
        Checked 0 service groups.
        Checked 1 contacts.
        Checked 1 contact groups.
        Checked 24 commands.
        Checked 5 time periods.
        Checked 0 host escalations.
        Checked 0 service escalations.
Checking for circular paths...
        Checked 2 hosts
        Checked 0 service dependencies
        Checked 0 host dependencies
        Checked 5 timeperiods
Checking global event handlers...
Checking obsessive compulsive processor commands...
Checking misc settings...

Total Warnings: 0
Total Errors:   0

Things look okay - No serious problems were detected during the pre-flight check

[root@ADV-CACTISERVER objects]# service nagios restart
Running configuration check...
Stopping nagios:. done.
Starting nagios: done.

refer

if you face error like NSClient - ERROR: Invalid password.  then refer