Sql connection C# login failed

i cannot connect via C# to my database and it's making me crazy.

I know my credentials are good because I can open my SQLServerMangement with them and query the database.

I always get login failed!!

I'm trying with a buch of different connection string and nothing works.

--> System.Data.SqlClient.SqlException (0x80131904): Login failed for user

        var connectionStrings = new List<string>();

        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=myuser;Password=mypassword");
        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=mydomain/myuser;Password=mypassword");
        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=mydomain\\myuser;Password=mypassword");
        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=mydomain\\\\myuser;Password=mypassword");
        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=mydomain//myuser;Password=mypassword");
        connectionStrings.Add("Data Source=myserver;Initial Catalog=mycatalog;User ID=mydomain\\myuser;Password=mypassword");


        foreach (var con in connectionStrings)
        {
            SqlConnection cnn ;
            cnn = new SqlConnection(con);
            try
            {
                cnn.Open();
                Console.WriteLine("Connection Open !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ");
                cnn.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Can not open connection ! ");
                //Console.WriteLine(ex.ToString());
            }

        }

The mydomain\myuser attempts indicate you might be using Integrated Security or Trusted_Connection. In that case, the connection string looks like this:

Server=myserver;Database=mycatalog;Trusted_Connection=True;

or this

Server=myserver;Initial Catalog=mycatalog;Integrated Security=True;

There is no combination here that allows you to specify a username or password. If you want to use a username/password, you must setup sql authentication and create a separate sql account. There is no way you can manually specify Active Directory or Windows login credentials to connect to a database, other than running the program as the user that is making the connection.