
Realistically, this is a rather frequent error error message. We shall learn how to “fix a network-related or instance-specific error occurred”. This error could mean different things as there is no one solution that fits all. Please see how to Migrate Your WordPress Site with WordPress Duplicator, how to Fix Spell Check Not Working in Microsoft Word, and how to Enable the End Task Option on the Windows 11 Taskbar. But in my case, it means that there is an issue with the network connectivity to the SQL Server instance as the name indicates.
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 is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26• Error Locating Server/Instance Specified) (Microsoft SQL Server)
Why was the error “A network-related or instance-specific error occurred”
As already discussed above, and from the error message below, the server could not be found or was not accessible. Yes, the instance name is correct but the SQL Server Service isn’t running. As a result, the following messages were prompted.

Even when you click on the show details tab, you cannot pinpoint the issue on the fly. Another indicative message from the image below is that is says “Cannot connect to MSSQL Instance”.

Also, see how to fix “the server was not found or was not accessible: Verify that the instance name is correct and that SQL Server is configured to allow remote connections“, and how to uninstall Microsoft SQL Server on Windows.
Resolve “error occurred while establishing a connection to SQL Server”
As you can see from the Services Manager, they are all not running.

To fix this, ensure the services Named instance as it is in my case or the default instance is running. All you need to do is right-click and start the service. There are numerous ways to start services on Windows.

As you can see below, these services are all applicable to me and as such are running again.

Now, initiate a connection again via the SSMS. The connection should be successful.

Here are some interesting articles: Unable to connect to MSSQL Server after changing the Server name, and how to fix “Cannot find the computer: Fix the following error occurred while using Kerberos authentication“.
Via the SQL Server Configuration Manager
Alternatively, to verify that the instance is running, select SQL Server Services in SQL Server Configuration Manager and check the symbol by the SQL Server instance.
- A green arrow indicates that an instance is running.
- A red square indicates that an instance is stopped.
If the instance is stopped, right-click the instance and select Start. Then, the server instance starts, and the indicator becomes a green arrow.
Via PowerShell commands
You can use the following command in PowerShell to check the status of SQL Server services on the system:
Get-Service | Where {$_.status -eq 'running' -and $_.DisplayName -like "sql server*"}

You can use the following command to search the error log file for the specific string “SQL Server is now ready for client connections. This is an informational message; no user action is required.”

As I said above, there is no one solution that fits all here. If the steps above do not resolve your issue, Please head over to the following Micorosft Page to see if any other area covered will resolve your issue. Please, see “Windows could not start the SQL Server service on local computer 17051: A network-related or instance-specific error occurred while establishing a connection to SQL Server“.
FAQs on Named and Default MSSQL instances
A Default Instance is the primary installation of SQL Server on a server, identified by the server’s hostname or IP address without specifying an instance name. A Named Instance is a secondary installation of SQL Server, identified by a specific name alongside the server’s hostname or IP address. Multiple Named Instances can coexist on the same server, each with its own set of databases and configuration
You can have only one Default Instance on a server. However, you can install multiple Named Instances, each with its own instance name and configurations, on the same server.
Named Instances allow you to run multiple independent SQL Server installations on a single server, each with its own databases, security settings, and configurations. This is useful for isolating applications, managing version compatibility, and optimizing resource utilization.
I hope you found this blog post helpful on how to Fix a network-related or instance-specific error occurred. Please let me know in the comment section if you have any questions.