@using (Html.BeginForm("DataCheck", "Home"))
        {
            <div class="inputGroup inputGroup1">

                <label id="adminLogin" for="adminlogin">Логин</label>
                @Html.TextBox("adminlogin", null, new { @class = "login" })


                <span class="indicator"></span>
            </div>
            <div class="inputGroup inputGroup2">
                <label id="adminPassword" for="adminpassword">Пароль</label>
                @Html.Password("adminpassword", null, new { @class = "password" })

            </div>
            <div class="inputGroup inputGroup3">
                <input type="submit" id="log_in" value="Войти" />
                <p> @ViewBag.Text </p>
            </div>

            <div class="login-close-popup js-login-close-campaign"></div>

        }

[HttpPost]
    public ActionResult DataCheck (string adminlogin, string adminpassword)
    {
        if(adminlogin == "Kate_adm" && adminpassword == "1234520")
        {
            return View("Admin_Page");
        }
        else
        {
            ViewBag.Text = "Неверно введены данные.";
            return View("Index");
        }

    }

http://localhost:49477/?adminlogin=Kate_adm&adminpassword=1234520