The error message is pretty explicit: the SQL server instance you are trying to connect to isn't there.
Start here: Simple SQL Connection String Creation
] and use Windows to establish a working connection string, then use that in your app.
But ... a couple of things on connection strings.
1) Don't hard code them. Connection strings are one the the things that should definitely change between dev and production - you should never test against production databases because ... well, isn't it rather obvious? So hard coding means you have to change every single time it's used when you release your software, and that means you are releasing untested software! Store them in a config file so that the string is not part of your app, and can be changed without altering your EXE. Have a look here: Instance Storage - A Simple Way to Share Configuration Data among Applications
] - it may help.
2) Never use the
account for general users: it's very dangerous. If your code is slightly wrong, or worse prone to SQL Injection, it gioves far, far too much power to the user. Connections should be made using a user with the minimum permissions they need to do their job - which does not include creating and deleteing databases!