uninstalling SambaPOS never fixes anything. Your dealing with a database. The database will still be there. You need to connect to the database and delete the database then restart sambapos so it will create a new one.
That being said please show us what is in the log file. It could be something else.
in Control Panel i see MIcrosoft SQL Server 2014. But i dont see under MS Services.
It is very interesting, i deinstall SQL Server from Control Panel, SAMPOS POS starts normally, BUT with Info: Sambapos is starting without Database, We recomended to use one. I install again SQL 2014, Sambapos doesnt start att all !
Your screenshot there shows sql localdb which is the version that comes in the samba installer.
This is the single user version, it doesnt run as a service only within the user session and only allows single terminal.
Personally even on a single terminal system I still install SQL Express (full version that runs as service) as im more familier with it, it comes with sql manager which you usually end up needing to download anyway to troubleshoot localdb.
SambaPOS without a connection string (what it would be after deleting the settings.txt would have no connection string and try to use localdb, after that it resorts to txt file which you definatly dont want to use.