First of all why you not share your connection string in question?
Sql Connection string in Windows Authentication. you can change as you want. like that
SqlConnection con= new SqlConnection("Data Source=your User Name or you can try .[dot];Initial Catalog=Database Name;Integrated" Security=True;Pooling=False");
Sql Server Authentication.
<connectionstrings>
<add name="MyDbConn">
connectionString="Server=MyServer; Database=pubs; User Id=MyUser; password= P@ssw0rd"
providerName="System.Data.SqlClient" />
</add></connectionstrings>
for more information hit this link
http://msdn.microsoft.com/en-us/library/ff648340.aspx
any query hit to reply.