ابتدا System.Management رو به References پروژه بیفزایید و سپس :
using System.Management;

private void GetHDDSerialNumber()
{
ManagementObjectSearcher searcher;
string query1 = "SELECT * FROM Win32_DiskDrive";
string query2 = "SELECT * FROM Win32_PhysicalMedia";

searcher = new ManagementObjectSearcher(query1);
foreach (ManagementObject wmi_HD in searcher.Get())
if (wmi_HD["Model"] != null)
MessageBox.Show(wmi_HD["Model"].ToString());

searcher = new ManagementObjectSearcher(query2);
foreach (ManagementObject wmi_HD in searcher.Get())
if (wmi_HD["SerialNumber"] != null)
MessageBox.Show(wmi_HD["SerialNumber"].ToString());
}