Private Sub Cbox_database_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cbox_database.MouseClick
    Try
        Dim frmloading As New loading
        loading.Show()
        cbox_database.Items.Clear()
        loadInstances(cbox_database)
    Finally
        loading.Close()
        cbox_database.DroppedDown = True
    End Try
End Sub

Sub loadInstances(cbox As ComboBox)
    Dim dt As DataTable = SqlDataSourceEnumerator.Instance.GetDataSources
    For Each dr As DataRow In dt.Rows
        cbox.Items.Add(String.Concat(dr("ServerName"), "", dr("InstanceName")))
    Next
End Sub