Not being able to set persistent cookie !!!

Hi all,
I am trying to set persistent cookie but not being able to.
I have 2 pages, login.aspx where user will login themselves and a default.aspx where user will be redirected once username and password is confirmed.

Login.aspx code is :-

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            HttpCookie objcookie = Request.Cookies["maincookie"];

            if (objcookie != null)
            {                
                Response.Redirect("Default.aspx");
            }
            else
            {
                Response.Redirect("login.aspx");
            }
        }
    }
    
    protected void btnsubmit_Click(object sender, EventArgs e)
    {
        if (txtusername.Text == "Akiii" && txtpassword.Text == "123")
        {
            HttpCookie objcookie = new HttpCookie("maincookie");
            objcookie["username"] = txtusername.Text;
            objcookie["password"] = txtpassword.Text;
            objcookie.Expires = DateTime.Now.AddDays(1);

            Response.Cookies.Add(objcookie);

            Response.Redirect("Default.aspx");
        }
        else
        {
            Response.Write("Please try again !");
        }
    }

And the default page code is:-

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            HttpCookie objcookie = Request.Cookies["maincookie"];

            if (objcookie != null)
            {
                usernameshow.Text = objcookie["username"];
                passwordshow.Text = objcookie["password"];
            }
            else
            {
                Response.Redirect("login.aspx");
            }
        }
    }

    protected void btnlogout_Click(object sender, EventArgs e)
    {
        HttpCookie objcookie = Request.Cookies["maincookie"];

        objcookie.Expires = DateTime.Now;
        Response.Cookies.Add(objcookie);       
        Response.Redirect("login.aspx");
    }

My problem is that, until and unless i click the logout button in the default page, the user should be able to access the website without doing login again...!

Please help me regarding this!

Thanks and Regards
Akiii