You have *still* not supplied a dmesg.
According to the limited information you've supplied so far, this is a used drive (with a valid MBR on it), and you failed to write to the drive while running fdisk as root.
Assuming that the above is true, wd0 is configured to be read-only. This is either by pin configuration on the drive electronics, or a setting in your BIOS, or some other hardware issue, such as a drive controller or drive configuration problem. It is not an ATA security setting, as you can read the MBR sector.
Check your BIOS settings. Check your pin configuration on the drive. Post a dmesg. Post the output of # atactl wd0 identify.