A old Acer computer with a broken hard disk. I replaced it and going to re-install Windows.

As you know nowadays all PC brands won't come with recovery disk. The recovery data is in a hidden partition inside the original hard-disk.

Although MS provided a way for user to download official iso images for free, however it doesn't support OEM product key.

Lucky I found a mirror site which hosting those iso images. After download the ISO file, do checksum and it is correct!