C# I can't show list in combobox : Good day!

I am a newbie in coding and I just want to get some help, I am trying to show a list in the combobox from sql, but I can't make it work, no errors, just my combobox is not showing anything, below is the code that I try to use.

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.Data.SqlClient;
    using Inventory.Properties;
    
    namespace Inventory
    {
        public partial class Form2 : Form
        {
            public Form2()
            {
                InitializeComponent();
            }
    
            SqlConnection conn = new SqlConnection(@"Data Source=MEDIXPC197;Initial Catalog=Inventory;Integrated Security=True");
    
            SqlCommand cd = new SqlCommand();
    
            
    
            public void cc()
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
    
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "SELECT Department from tbldept";
                cmd.ExecuteNonQuery();
                DataTable dt = new DataTable();
                SqlDataAdapter Da = new SqlDataAdapter(cmd);
                Da.Fill(dt);
                foreach (DataRow dr in dt.Rows)
                {
                    comboBox1.Items.Add(dr["Department"].ToString());
          
    
                }
    
    
                conn.Close();
            }
    
            private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "select Department from tbldept";
                cmd.ExecuteNonQuery();
                DataTable dt = new DataTable();
                SqlDataReader dr = cmd.ExecuteReader();
                {
                    comboBox1.Items.Add(dr.GetValue(0));
                }
            }
        }
    }

just new in coding guys, please be gentle =)