The first and most basic step after a SQL Server installation or upgrade is to make sure the appropriate network protocols are configured on the server.
Note that the term server is used here to refer to an instance of the SQL Server 2012 Database Engine. The term client is used generally to mean any program that needs to communicate with a server. The server and client may reside on the same physical machine (especially when using SQL Server Compact and Express Editions).
First, you should ensure that the protocols your clients once used to connect to SQL Server 7, 2000 or 2005 (or that your clients would like to use) are still supported by SQL Server 2012 and are configured.
You might be surprised to learn that ...