A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. text
Generally issues like this are related to any of the following need to be looked at:
- firewall settings from the web server to the database server
- connection string errors
- enable the appropriate protocol pipes/ tcp-ip
Try connecting to sql server with sql management server on the system that sql server is installed on and work from there. Pay attention to information in the errorlogs.