Without exact system info nobody can realyl tell you much. These issues tend to occur when system settings override or conflict with PS and it can't correctly detect the default settings used by the computer.
Thank you both, but I couldn't create the manifest file in the registry, because the subfolder specified in the instructions didn't exist.
HOWEVER, I did finally figure it out, glory be.
1. Create a shortcut icon on your taskbar if you don't already have one.
2. Right-click on the icon,and you will see:
- the Photoshop icon
-Unpin from Taskbar Window
3. Hover the mouse over the Photoshop icon and right-click again, and the "Properties" option will be at the bottom
4. A dialog box will open, and under "Settings" is an option to "Override high DPI scaling behavior. Scaling performed by:"
5. Check it. You don't have to specify the application because you already did by using the Photoshop icon.