private void Submenu_Login_Click(object sender, EventArgs e)
 {
     if (lgn == null)
     {
         lgn             = new FormLogin();
         lgn.MdiParent   = this;
         lgn.FormClosed += new FormClosedEventHandler(lgn_FormClosed);
         lgn.Show();
     }
     else
     {
         lgn.Activate();
     }
 }
 void lgn_FormClosed(object sender, FormClosedEventArgs e)
 {
     lgn = null;
 }