Either your data string is wrong if so just change in that box
More than likely your SQL service has stopped and you just need to start it in Task Manager > Services > open services
Then click on the sql server you need and click start, once started run samba again and it will open
We provided support to him. There was 2 instances of SQL Server installed and the wrong one had started, stopping the correct instance from starting (as they were set on the same TCP port). So it was just a matter of stopping the incorrect instance and starting the correct instance.
Unsure why 2 instances of SQL server were installed, the other instance had no databases so we just removed it.