You will need a third party software to make it fully workable for Windows 10 version. More of a challenge if you have a earlier version of Windows. The key is being able to have compatible hardware . i. e You have to match both hard drives either IDE or SATA. If it was me, I would just clone the data from the failing hard drive using a USB thumb drive and then once a new hard drive is selected, format and partition with a clean downloadable copy of Windows operating system. Contact Window's Support team for a re-install of the one you are now using and start fresh. Once working and as the primary hard drive in the computer, attach the thumb drive and move the data or make a slave hard drive as you suggested and put it in the computer and initialize it using the Windows Tools and make it the slave. Once completed and installed with proper jumpers and cables, just cut and paste files, but I would create a new directory on the drive that is different from the folder containing the operating system files. Hope this helps...if not there are other ways. Be sure the old hard drive you get from another computer is the same as the one you want to use since the newer drives have different connectors and jumpers and depending on the age of you current mother board, may not be compatible connector-wise and power wise.

I have enclosed a video that might give you some ideas.
https://www.easeus.com/todo-backup-resource/clone-bootable-hard-drive.html