The problem most of the time is that Windows 8.1 has secure boot. Secure boot severely limits the graphics cards that you can configure onto your system. If you can get your system to boot without secure boot, you have a much better chance of getting upgraded graphics cards configured. See your system BIOS for these boot/startup settings.
My Lenovo K450e system has Windows 8.1, and has secure boot turned on. That's why I bought the K450e model that has the GTX 760 standard. That graphics card is good enough for me.