Access LAN Computer with Local Administrator using Windows Management Instrumentation (WMI).
Follow below setting for every LAN Computer you want to access.
Settings:

• Go to Control Panel
• Open Windows Firewall
• Open Inbound Rules
• Enable Windows Management Instrumentation (WMI-In) for domain profile.

ManagementNamedValueCollection mContext = new ManagementNamedValueCollection();
mContext.Add("__ProviderArchitecture", 64);
mContext.Add("__RequiredArchitecture", false);
ConnectionOptions options = new ConnectionOptions();
ManagementScope ManagementScope1 = new ManagementScope();
bool isConnect = false;
try
{
options.Username = Local Administrator UserId;
options.Password = Local Administrator Password;
options.Authority = "ntlmdomain:DOMAIN";
options.Impersonation = ImpersonationLevel.Impersonate;
options.EnablePrivileges = true;
options.Context = mContext;

ManagementScope1 = new ManagementScope(string.Format("\\\\{0}\\root\\cimv2", "IP Address"), options);
ManagementScope1.Connect();
isConnect = true;
}
catch (Exception ex)
{
}