OLEDB Connection problem in C#

I am working with C# windows application and I am facing a problem with OLEDB connection to SQL SERVER 2008 my code is too simple: I am trying to fill the datagridview from this query

string connString = "Provider=SQLOLEDB;Data Source=servername;Initial Catalog=DBname;Integrated Security=SSPI";

        string query = "SELECT * FROM account";

        //create an OleDbDataAdapter to execute the query
        OleDbDataAdapter dAdapter = new OleDbDataAdapter(query, connString);

        //create a command builder
        OleDbCommandBuilder cBuilder = new OleDbCommandBuilder(dAdapter);

        //create a DataTable to hold the query results
        DataTable dTable = new DataTable();

        //fill the DataTable
        dAdapter.Fill(dTable);

        //the DataGridView
        //DataGridView dgView = new DataGridView();

        //BindingSource to sync DataTable and DataGridView
        BindingSource bSource = new BindingSource();

        //set the BindingSource DataSource
        bSource.DataSource = dTable;

        //set the DataGridView DataSource
        dataGridView_FraudDetails.DataSource = bSource;
        dAdapter.Update(dTable);

but I get the Following error in this line

//fill the DataTable
        dAdapter.Fill(dTable);

"[DBNETLIB][ConnectionOpen (Connect()).]SQL Server does not exist o开发者_开发技巧r access denied." The code was running well , but when I uninstalled the server and reinstalled it again it gave me that error

I tried to turn off the firewall but it doesn't work any suggestion please

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Are you using SQL Server Express? If so you need to make sure that it is configured to accept connections via either TCP/IP or named pipes. By default, SQL Server Express does not accecpt connections. See http://www.datamasker.com/SSE2005_NetworkCfg.htm (this page is specific to SQL Server 2005 but should apply to 2008 as well).

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Go to SQL Server Configuration Manager (under All Programs > Microsoft SQL Server in start menu) and for your instance, make sure TCP/IP is enabled. It is disabled by default for a new install of SQL Server.