cant insert into my database

Question

hi,

im making a page where users click on the "REGISTER" button to register into the program. the program gives the user a username by taking the first 3 characters of the first name and first 3 characters of the last name. if the username already exists i just add an incrementing number to it, for example username1, username2..etc.

i dont get any error when i run this code but its not inserting it into the database either and i cant figure out what the problem is.
Any help is greatly appreciated!
thanks from now!

[code]
private void button1_Click(object sender, EventArgs e)
        {
            System.Data.SqlClient.SqlConnection con = new SqlConnection();
            con.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=|DataDirectory|\\AltarianChessDB.mdf;Integrated Security=True;User Instance=True";

            con.Open();

            SqlDataAdapter da = new SqlDataAdapter("SELECT Username from Players", con);
            DataTable dt1 = new DataTable();
            da.Fill(dt1);

 string uname = firstnametxt.Text.Substring(0, 3) + secondnametxt.Text.Substring(0, 3);
            bool found = false;

            int j=0;

            for (int i = 0; i < dt1.Rows.Count; i++)
            {
                if (dt1.Rows[i][0].ToString().Substring(0,6) == uname)
                {
                    found = true;
                    j=i;
                }
            }

            if (found == true)
            {
                string numstring = dt1.Rows[j][0].ToString().Substring(6, dt1.Rows[j][0].ToString().Length);
                int num = Convert.ToInt16(numstring) + 1;
                numstring = num.ToString();
                uname = uname + numstring;

            }
            con.Close();
            con.Open();
            int creditvalue = 30;
           
            System.Data.SqlClient.SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
           
cmd.CommandText=("insert into Players (Username,FirstName,SecondName,PlanetOfOrigin,Password,Credit) values ('"+uname+"','"+firstnametxt.Text.Trim()+"','"+secondnametxt.Text.Trim()+"','"+planetoforigintxt.Text.Trim()+"','"+passwordtxt.Text.Trim()+"','"+creditvalue+"')");
            cmd.ExecuteNonQuery();
             MessageBoxButtons buttonTyperegistered = MessageBoxButtons.OK;
            MessageBoxIcon iconTyperegistered = MessageBoxIcon.Information;
            DialogResult resultregistered = MessageBox.Show("You've successfully registered to play!\n Your username is " + uname, "Altarian Chess", buttonTyperegistered, iconTyperegistered, 0, 0);
           
           con.Close();

            Form4 frm4 = new Form4();
            frm4.Show();
            frm4.Visible = true;

            Form3 frm3 = new Form3();
            frm3.Hide();
            frm3.Visible = false;
 
        }

[/code]