The connection string you are using is wrong.
Please try to use the correct one according to your configurations.
For that you have one awesome website -
http://www.connectionstrings.com/[
^].
Search for the required connection string according to the database and technology.
For Example (SQL Server 2008) -
Connection strings for SQL Server 2008[
^].
Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;
For Local DB, you can just provide a dot "." instead of
(localdb)\v11.0.
So, you can try with the below one...
Server=.;Database=Practice;User Id=myUsername;Password=myPassword;
Provide necessary UseName and Passwords.