Try this, uninstall SambaPOS delete the folder that has the settings.txt file. Find and remove SQL Server localdb. You can usualy see it in add/remove program files. Then reinstall sambapos and choose localdb 2014 or you can opt to install SQL Express 2014 instead and use a connection string. I highly recommend installing full SQL its easier to troubleshoot.
If you install full sql then uncheck the localdb install option. Download and install SQL Express 2014 and follow this tutorial to set it up:
This tutorial goes with the SQL Express one it solves most issues with SQL Express