Insert not taking effects in Database

Question

Hello everyone!
I have a slightly problem. I want to insert a row in database during the running program. After clicking the button I have no error but when that form close I can"t see row inserted, it"s not in database. But i want to visualise from the same form where i insert i can see row. After closing it, the row disappear. Please help! Why is not commiting in database, why it is not inserting in database too?

Here is my code: 

try
            {
               detaliiviz_form.connect.Open();
                SqlCommand cmd = new SqlCommand("INSERT INTO Detinute([cod_caracteristici],[marca],[perioada],[tara]) VALUES(@cod_caracteristici,@marca,@perioada,@tara)",detaliiviz_form.connect);
                cmd.Parameters.AddWithValue("@cod_caracteristici","ete");
                cmd.Parameters.AddWithValue("@marca", modifprof_form.listview.SelectedItems[0].SubItems[3].Text.Trim());
                cmd.Parameters.AddWithValue("@perioada", dP_per1.Value.ToString("dd/mm/yyyy", CultureInfo.InvariantCulture) + "-" + dP_per2.Value.ToString("dd/mm/yyyy", CultureInfo.InvariantCulture));
                cmd.Parameters.AddWithValue("@tara", tb_taraprof.Text.Trim());
                cmd.ExecuteNonQuery();
                detaliiviz_form.connect.Close();
            }
            catch(SqlException ex)
            {
                MessageBox.Show(ex.ToString());
            }
            this.Close();