how to get the all computers list connected to network

Of many articles on LAN network here at CP itself, this one should meet your needs: A collection class for listing all the computers and servers in your network, with category information[^]

Please use CP articles repository, it has great many articles. A simple search can provide you much more in case you need.

Similar questions asked earlier and answered: get ipp address of all pcs connected via lan [^]

0) I found this code on msdn, but if you're on a corporate/military network, you may not be able to get the desired output:

using System.Diagnostics;  
using System.IO;  
  
//Gets the machine names that are connected on LAN  
Process netUtility = new Process();  
netUtility.StartInfo.FileName = "net.exe";  
netUtility.StartInfo.CreateNoWindow = true;  
netUtility.StartInfo.Arguments = "view";  
netUtility.StartInfo.RedirectStandardOutput = true;  
netUtility.StartInfo.UseShellExecute = false;  
netUtility.StartInfo.RedirectStandardError = true;  
netUtility.Start();  
  
StreamReader streamReader = new StreamReader(netUtility.StandardOutput.BaseStream, netUtility.StandardOutput.CurrentEncoding);  
  
string line = "";  
  
while ((line = streamReader.ReadLine()) != null)  
{  
      if (line.StartsWith("\\"))  
      {  
           listBox1.Items.Add(line.Substring(2).Substring(0, line.Substring(2).IndexOf(" ")).ToUpper());  
      }  
}  
  
streamReader.Close();  
netUtility.WaitForExit(1000);  

1) You could do a ping sweep, but that would take forever, and if the Windows firewall is enabled on any of the boxes, it may be configured to refuse ICMP requests, and you're stuck - again.

2) Insteat of using net.exe in the first example, you could use nMap.exe. Google for the commandline parameters.