If you try to use the drivers intended for the newer "Intuos" line or the "One" line, your CTH-670 will likely not be recognized. You must use a specific legacy driver. While Windows 10 is generally good at backward compatibility, it does not always install the correct Wacom driver automatically via Windows Update. If it does, it usually installs a generic HID driver that treats your tablet like a mouse, disabling pressure sensitivity in Photoshop, Clip Studio Paint, and Krita.
Then her PC auto-updated to Windows 10.
The key to a stable setup on Windows 10 is using , which remains the most compatible official legacy driver for this specific model. Step-by-Step Installation Guide