Hello and thank you for your question. I look forward to assisting you today. What type of an external reader did you buy for the old HDD?
Excellent reader! You cannot simply install that drive as the boot drive due to the hardware differences. What you can do is install it as the secondary drive and access the files from there.
Well sort of. When you install Windows, it correlates the machines hardware into a nice little bundle the operating system recognizes from that time forward. It also communicates that information to Microsoft as well to tie your activation key in with the hardware. If you were to try to take the drive as it is now and install it into an existing computer and boot from it, it would fail. If you install it as a secondary device, and because you don't have to boot from it, that drive has now become just a storage area for files that you can access. You could make it a boot drive again, but you would have to re-partition and format it then install a new copy of Windows on it, but that would wipe all of your files.
Correct. You cannot use it as a boot drive in any other computer other than the original it was installed and configured for. You can install it as a secondary drive in anything you want and access the files that way.
Still with me?