how can t connect to the wright database

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Visual-Studio

dear sir;
when i run my website on visual studio . it gives me error
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A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;


public partial class WUC_Register1l : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void Buttonregister_Click(object sender, EventArgs e)
{

// declaration
SqlConnection conn = new SqlConnection ();
SqlCommand cmd = new SqlCommand();

//required
conn.ConnectionString=ConfigurationManager.ConnectionStrings[1].ToString() ;

cmd.Connection = conn;
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "ManageMember";
cmd.Parameters.AddWithValue("@check", "a");
cmd.Parameters.AddWithValue("@username", Txtusername.Text);
cmd.Parameters.AddWithValue("@password", Txtpass.Text);
cmd.Parameters.AddWithValue("@name", Txtname.Text);
cmd.Parameters.AddWithValue("@email", Txtmail.Text);
cmd.Parameters.AddWithValue("@phone", Txtphone.Text);
cmd.Parameters.AddWithValue("@company", Txtcompany.Text);
cmd.Parameters.AddWithValue("@gender", RadioButtongender.SelectedValue);
cmd.Parameters.AddWithValue("@birthday", Txtbirthday.Text);
cmd.Parameters.AddWithValue("@qustion", Txtquestion.Text);
cmd.Parameters.AddWithValue("@answer", Txtanswer.Text);




//DB work
conn.Open();
try
{
cmd.ExecuteNonQuery();
lblmsg.Text = "User Added Successfully";
}
catch(SqlException ex)
{
if (ex.Number == 2627)
lblmsg.Text = "Username already exists,Please changepassword Username";
else
lblmsg.Text = ex.Message;
}
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my mail is : nanat111@yahoo.com