On the button click i have written this code
and it start working
DataTable dt = new DataTable();
SqlCommand cmd = new SqlCommand(" select * from magazinesectionmaster where mid =" + comboBox1.SelectedValue.ToString() + " order by section_name", sc);
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(dt);
dataGridView1.DataSource = dt;
dataGridView1.Visible = true;