Data source=[Computer name]\SAMBAPOS4; User Id=sa; Password=sambapos
[Computer name] : same name as your computer , to see the computer name go to Control Panel\System and Security\System
Computer name: Under Computer name, domain, and workgroup settings, you can find your computer name,
Following details needs to be same as configured during SQL configuration.
SAMBAPOS4; User Id=sa; Password=sambapos
You can also refer to the guide john has created.