Retrieve Data Value which is transfer from one form to another by post method in asp.net

We can access form post value using Request.Form["parametername"] and the code are given below have a look on this topic and try this.......

if(Request.Form !=null)
{
    string name = Request.Form["name"].ToString();
    string email = Request.Form["email"].ToString();
    string mobile = Request.Form["mobile"].ToString();
    string city = Request.Form["city"].ToString();
    string state = Request.Form["state"].ToString();
}

Find window forms attached by MDI Parent in C#

Try this code to close perticular open form or all open form.......

foreach (Form form in Application.OpenForms)
                            {
                                if (form.Name == "Login")
                                {
                                    form.Close();
                                }
                             // /* to close all open form */
                             //  form .Close();
                            }

Prevent Window form to Open when Same form Open Already

Try this code on Window(Form) Open Events it will close open form and open new form/window........

var form1 = new Formname();
                var openedForm = Application.OpenForms[form1.Name];
                if (openedForm != null)
                {
                    openedForm.WindowState = FormWindowState.Normal;
                    openedForm.BringToFront();
                    openedForm.Activate();
                }
                else
                {
                    // If required.
                    form1.MdiParent = this;
                    form1.Show();
                }