procedure TForm1.FormCreate(Sender: TObject);
var
 RawMBR: array[0..511] of Byte;
 btsIO: DWORD;
 hDevice: THandle;
 Serial: string[9];
begin
 //PhysicalDrive0 or  C:
 hDevice := CreateFile('\\.\C:', GENERIC_READ,
   FILE_SHARE_READ or FILE_SHARE_WRITE, nil, OPEN_EXISTING, 0, 0);
 if hDevice <> INVALID_HANDLE_VALUE then
 begin
   // each sector has 512 Bytes
   // replace 0 with sector that you wish to read
   SetFilePointer(hDevice, 512 * 0, nil, FILE_BEGIN);
   ReadFile(hDevice, RawMBR[0], 512, btsIO, nil);
   CloseHandle(hDevice);
   Serial := Format('%x%x%x%x', [RawMBR[75], RawMBR[74], RawMBR[73],
     RawMBR[72]]);
   ShowMessage(Serial);
   ShowMessage(IntToStr(btsIO));
   //WriteFile!(0,rawmbr[72],4,btsIO,nil);
 end;
end;  

Function GetHDDSerial: String;
var
  RawMBR: array[0..511] of Byte;
  btsIO: DWORD;
  hDevice: THandle;
  Serial: string[9];
begin
  Result := '';
  //PhysicalDrive0 or  C:
  hDevice := CreateFile('\\.\C:', GENERIC_READ,
    FILE_SHARE_READ or FILE_SHARE_WRITE, nil, OPEN_EXISTING, 0, 0);
  if hDevice <> INVALID_HANDLE_VALUE then
  begin
    // each sector has 512 Bytes
    // replace 0 with sector that you wish to read
    SetFilePointer(hDevice, 512 * 0, nil, FILE_BEGIN);
    ReadFile(hDevice, RawMBR[0], 512, btsIO, nil);
    CloseHandle(hDevice);
    Serial := Format('%x%x%x%x', [RawMBR[75], RawMBR[74], RawMBR[73],
      RawMBR[72]]);
    Result := Serial;
    //ShowMessage(Serial);
    //ShowMessage(IntToStr(btsIO));
    //WriteFile!(0,rawmbr[72],4,btsIO,nil);
  end;
end;