unable to find my sql server express sample database through connection in c#?

hello, recently i started an ado.net project using my visual studio community edition, i created a CommerceDBDemo database project and published it, and i started another ado.net project trying to connect to that db through 

    SqlConnection sqlconn=new SqlConnection();

    SqlConnectionStringBuilder sqlConnStringBuilder =new SqlConnectionStringBuilder();

     // connection string detail omited due to no cut and paste function on yahoo, and slow to type manually.

    sqlconn.open() //throw sql exception, saying failure to find and connect to database

my question is, what are the problems, for example, if the database publishing is wrong or incomplete, anyway, thanks