Thanks for the new info. Based on what you've added, I don't think you need to use shadow files (which take time to generate and slow PD down while it's creating them), and I also don't think uninstalling/reinstalling PD will make any difference.
Assuming you're not looking to get a new computer, using the
Reset this PC tool or doing a clean installation of Windows may be the only ways to solve this particular issue. Here's a link to the
steps, which will give you the option to keep all your data files and (most) of the installed apps or to completely start over.
Make sure you have all your old installers, CDs and DVDs ready, and it's always a good idea to make a full system backup that's stored on external discs or USB drives in case you need to recover any missing files.
Since we're talking about some significant changes here, I also think it's important to consider updating to a modern version of Windows.
Your system isn't compatible with Win11, but Win10 is a far better OS than 8.1, especially since MS stopped mainstream support for that version three years ago and will end all support in Jan 2023 (15 months from now).
You could try an in-place upgrade from 8.1 to 10 first and see how that goes, and only doing a clean Win10 installation and adding back all your apps if PD16 was still lagging.