connection error plz help me out

hai all as iam doing vb application .by using sqlserver 2005 after debuging its shwoing me this error can any one plz tell me how to provide connection ????
as i paste coding that i wrote for sample application

ERROR::getting this error so plz tell me how to overcome this error ....

An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)


coding ..............



Imports System
Imports System.Data
Imports System.Data.SqlClient
Public Class Form1
Dim dr As SqlClient.SqlDataReader
Dim connectionstring As String = System.Configuration.ConfigurationSettings.AppSettings("DBCon")
Dim cn As New SqlConnection(connectionstring)
Dim dt As New DataTable
Dim ds As New DataSet
Dim adap As New SqlDataAdapter
Dim cmd As New SqlCommand
Dim sqlquery As String = ""
Private Sub btnsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsave.Click
If cn.State = ConnectionState.Closed Then cn.Open()
' cn.Open()
sqlquery = "insert into tbl_siri(sname,saddress) values('" & txtname.Text & "','" & txtadd.Text & ")"
cmd = New SqlCommand(sqlquery, cn)
cmd.ExecuteNonQuery()
MsgBox("successfully saved...")
End Sub

Private Sub btnclear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnclear.Click
txtadd.Text = ""
txtname.Text = ""
End Sub
End Class


in app config------------






// as there is no id and pwd  as iam doing using windows authentication so shall i want to mention id n pwd here r not