Write the following code in Button click event

 protected void Button1_Click(object sender, EventArgs e)
    {

        con.Open();
        SqlDataAdapter adp = new SqlDataAdapter("select * from com_register where uname='" + TextBox1.Text + "' AND pass='" + TextBox2.Text + "'", con);
        System.Data.DataTable dt = new DataTable();


        adp.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            Session["login"] = dt.Rows[0][0].ToString();


            Response.Redirect("Default.aspx");

        }
        else
        {
            System.Windows.Forms.MessageBox.Show("User name or password is wrong", "Information", System.Windows.Forms.MessageBoxButtons.OK, System.Windows.Forms.MessageBoxIcon.Warning);

        }
      


    }