How to resolve the issue of SQL Server being unable to connect to the server?

There could be various reasons and solutions if SQL Server cannot connect to the server.

1. Make sure that the SQL Server service is running: ensure that the SQL Server service is started by checking in the Windows Services and starting it if necessary.
2. Check the network connection: make sure the connection is working properly, you can try using the ping command to test the server’s IP address to see if it can connect successfully.
3. Check the firewall settings: The firewall may be blocking the connection to SQL Server. On the server, open the firewall settings and make sure to allow SQL Server to use the necessary ports.
4. Check the SQL Server configuration to make sure that remote connections are enabled. You can use SQL Server Configuration Manager to review and modify the settings.
5. Check the connection string: If connecting to SQL Server through an application, make sure that the server name or IP address, username, and password in the connection string are correct.
6. Check the port settings of SQL Server: By default, SQL Server uses port 1433. If another program is using this port, it may cause connection issues. You can try changing the port number for SQL Server.
7. Check the login permissions for SQL Server: Make sure that the login user being used has the appropriate permissions to connect to SQL Server. You can check and change user permissions in SQL Server Management Studio.

If the above methods still cannot solve the problem, you can try reinstalling SQL Server or contact the database administrator or technical support for assistance.