The database exists at all most likely because your application code creates a default database when one is not found. This is the default implementation for EF Code First with Migrations enabled.
So, where did my database tables go?
Reformatting cleared everything, but it looks like your code doesn't have the necessary migration steps configured to create the needed tables, or your migration strategy is not setup to automatically upgrade to the latest version.
Another issue that is harder to notice the first time, if migrations are not managed carefully, especially at the start of a project or when this is your first Code-First project, if there is a SQL or other Exception raised during migration executions, then the migrations will no be executed.
I would first try to run the following command in the package manager console:
update-database
Simple I know... If you have automatic migrations enabled in the code, but you don't handle the exceptions that are raised, then it will just look to the user as if the app didn't load. So execute the migrations from within VS and inspect the output.
If there are no migrations to apply, then either there are no migrations in your code to actually apply, which might mean that you were managing the database schema manually or via another technique, or something else has gone wrong with configuration, this is entirely subjective to your specific project environment, and way out of scope for an SO post.
However... You could short-circuit all that and run the following to try and generate a new migration to take you from zero, to where your coded schema is now:
add-migration AfterFormat
If this generates a new migration script that is empty, then there are no changes, if this is the case, then you are simply using the wrong connection string or there are no tables defined in your EF DbContext...
.