C#

string LOU = (queryObj["UserName"].ToString());
string[] LOUser = LOU.Split('\\');
string logonuser = (LOUser[1]+"@"+LOUser[0]);//have also tried (LOUser[1].Trim()) - (LOUser[1].Replace(" ","").Trim())- (LOUser[1].Trim().Replace(" ","")+"@"+LOUser[0])
WindowsIdentity wi = new WindowsIdentity(logonuser)

CCodeNewbie wrote:

giving non-useful errors.

using Microsoft.Win32;
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Diagnostics;
using System.IO;
using System.Management;
using System.Net;
using System.Net.NetworkInformation;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Text;
using System.Threading;
using System.Timers;
using System.Windows.Forms;

namespace MyProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                ManagementObjectSearcher searcher = new ManagementObjectSearcher("root\\CIMV2", "SELECT * FROM Win32_ComputerSystem");
                foreach (ManagementObject queryObj in searcher.Get())
                {
                    string LOU = (queryObj["UserName"].ToString());// returns domain\username
                    Console.WriteLine(LOU);
                    Console.ReadLine();
                    WindowsIdentity wi = new WindowsIdentity(LOU);// ref http://msdn.microsoft.com/en-us/library/ms998351.aspx#paght000023_impersonatingbyusingwindowsidentity
                    WindowsImpersonationContext ctx = null;
                    ctx = wi.Impersonate();
                    WindowsPrincipal wp = new WindowsPrincipal(wi);

                    string AuthType = wi.AuthenticationType;
                    string Authd = wi.IsAuthenticated.ToString();
                    string isGuest = wi.IsGuest.ToString();
                    string SidNo = wi.Owner.ToString();
                    string SidPlain = wi.Owner.Translate(typeof(System.Security.Principal.NTAccount)).ToString();
                    string Token = wi.Token.ToString();

                    Console.WriteLine(AuthType);
                    Console.WriteLine(Authd);
                    Console.WriteLine(isGuest);
                    Console.WriteLine(SidNo);
                    Console.WriteLine(SidPlain);
                    Console.WriteLine(Token);

                    foreach (System.Security.Principal.IdentityReference group in wi.Groups)
                    {
                        Console.WriteLine(group.Translate(typeof(System.Security.Principal.NTAccount)));
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
        }
    }
}

[DllImport("user32.dll", EntryPoint = "GetClassNameA")]
        public static extern int GetClassName(IntPtr hwnd, StringBuilder lpClassName, int nMaxCount);
        /*delegate to handle EnumChildWindows*/
        public delegate int EnumProc(IntPtr hWnd, ref IntPtr lParam);
        [DllImport("user32.dll")]
        public static extern int EnumChildWindows(IntPtr hWndParent, EnumProc lpEnumFunc, ref  IntPtr lParam);
        [DllImport("user32.dll", EntryPoint = "RegisterWindowMessageA")]
        public static extern int RegisterWindowMessage(string lpString);
        [DllImport("user32.dll", EntryPoint = "SendMessageTimeoutA")]
        public static extern int SendMessageTimeout(IntPtr hwnd, int msg, int wParam, int lParam, int fuFlags, int uTimeout, out int lpdwResult);
        [DllImport("OLEACC.dll")]
        public static extern int ObjectFromLresult(int lResult, ref Guid riid, int wParam, ref IHTMLDocument2 ppvObject);
        public const int SMTO_ABORTIFHUNG = 0x2;
        public Guid IID_IHTMLDocument = new Guid("626FC520-A41E-11CF-A731-00A0C9082637");

int i = SendMessageTimeout(hWnd, lngMsg, 0, 0, SMTO_ABORTIFHUNG, 1000, out lRes);
                        if (lRes != 0 && i !=0)

If the function succeeds, the return value is nonzero.

using System;
using System.Runtime.InteropServices;

internal static class NativeMethods
{
    public const int SMTO_NORMAL = 0x0000;
    public const int SMTO_BLOCK = 0x0001;
    public const int SMTO_ABORTIFHUNG = 0x0002;
    public const int SMTO_NOTIMEOUTIFNOTHUNG = 0x0008;
    public const int SMTO_ERRORONEXIT = 0x0020;

    // http://msdn.microsoft.com/en-us/library/windows/desktop/ms644952(v=vs.85).aspx
    /*
LRESULT WINAPI SendMessageTimeout(
__in       HWND hWnd,
__in       UINT Msg,
__in       WPARAM wParam,
__in       LPARAM lParam,
__in       UINT fuFlags,
__in       UINT uTimeout,
__out_opt  PDWORD_PTR lpdwResult
); */
    [DllImport("User32.dll", SetLastError = true)]
    public static extern IntPtr SendMessageTimeout(
        IntPtr hWnd,
        int Msg, // could use uint
        IntPtr wParam,
        IntPtr lParam,
        int fuFlags, // could use uint
        int uTimeout, // could use uint
        out IntPtr lpdwResult);
}

The value of this parameter depends on the message that is specified.