TITLE: Error ------------------------------ A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server

That error means that you were no able to reach the SQL Server instance you specified. There can be any number of reasons:

• Server and/or instance name misspelled.
• SQL Server is not running.
• You are blocked by a firewall.
• You have installed only SQL Server Management Studio, and you need to install SQL Server as well.
• And the list goes on.

Overall, it is difficult to help with this error when you give no context of to why you expect connection to work.