at the same time a lot of people to open a website in asp.net

namespace mekmersite.admin
{
    public class Kullanici
    {

        private bool _kontrol;

        public bool Kontrol
        {
            get { return _kontrol; }
            set { _kontrol = value; }
        }

        private bool _btClick;

        public bool BtClick
        {
            get { return _btClick; }
            set { _btClick = value; }
        }

        public Kullanici()
        {
            this.BtClick = false;
        }

        public void Kontrolet(string kullanici,string sifre)
        {
            string sorgu = "SELECT COUNT(*) FROM LOGIN WHERE USERNAME='" + kullanici + "' AND PASSWORD='" + sifre + "'";
            if (Metotlar.Connection.Komut.IntegerVeriOku(sorgu, 0) > 0)
                this.Kontrol = true;
            else
                this.Kontrol = false;
        }
    }
}

public partial class login : System.Web.UI.Page
{
    //VeriServisi.KullaniciKontrolClient veri = new VeriServisi.KullaniciKontrolClient();
    admin.Kullanici kn = new admin.Kullanici();
    //protected void Page_PreRender(object sender, EventArgs e)
    //{
    //}

    protected void ASPxButton1_Click(object sender, EventArgs e)
    {

        kn.Kontrolet(txt_username.Text, txt_pass.Text);
        if (kn.Kontrol)
        {
            FormsAuthentication.RedirectFromLoginPage(txt_username.Text, true);
            Response.Redirect("~/Default1.aspx");
        }
        else
            Response.Write("Yanlış Giriş Yaptınız");

    }
}