re-call login form from main form menu item,BUT HOW?

hi ali,
The codes that I tried to do this work.
I call main form from Program.cs

       [STAThreadAttribute]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new frmMainForm());
 }
I added the login form calling code into the main form constructor
        public frmMainForm()
        {
            InitializeComponent();
    
            frmUserLogin fUserLogin = new frmUserLogin();
            fUserLogin.ShowDialog();
 
        }
The login form OK button code that I added is below
private void btnLogin_Click(object sender, EventArgs e)
        {
     //in this area I am checking USername and password textboxes and etc.
    // .... 
           if (sPassword == txtPassword.Text)
            {

                this.Close();
            }
            else
            {
                MessageBox.Show("Geçersiz sifre", CGlobalVars.FCaption, MessageBoxButtons.OK, MessageBoxIcon.Warning);
                txtPassword.Focus();
                return;
            }
  
      if (GetPermissions() == false)     // this if block is getting the menu item      {    
        //permissions
           
                return;
            }
      }
and I added this code to my menuitem click event and Application.Restart() method here.
      private void tsmiChangeUsers_Click(object sender, EventArgs e)
        {
                frmUserLogin fUserLogin = new frmUserLogin();
                fUserLogin.ShowDialog();
         
               Application.Restart ();
     }

These are the my running steps for program.
1.run program
2.enter username and pasword on login form.
3.call mainform and give permissions for menuitems which username is used.(if admin,give all permissions,else restrict
permissions menu items' visibility)
4.now i want to change user when my main form is still on the screen.I call login from menuitem click.
5.after i have pressed login button on login form,load main form with new users rights and menu items permissions.
Till 4th step,it is OK but i couldnt figure out the fifth.when i run 5th step,the permissions belong to previous user.
How could I do this scenario.
Thanks in advance.
Kerem

Dear Kareem,
Please restart the application As the user click on the menu "mnuChangeUser"   LIKE
System.Windows.Forms.Application.Restart();