@nexiumn
It is always a good idea to post the exact HardwareIDs of the related graphics device (right-click onto it > “Properties” > “Details” > “Property” > "HardwareIDs).
I doubt, that you will find any WHQL certified Intel UHD Graphics driver, which supports
a) your specific on-board graphics adapter with the DeviceID DEV_9A78 and
b) Windows 8.1.
AFAIK the latest Win8.1 compatible Intel HD graphics driver is the v9.17.10.4229 one dated 05/26/2015 (as part of the Set v15.28). Maybe you will get it working by forcing its installation.
This the way how to get a graphics driver manually installed, whose *.INF doesn’t contain the DeviceID of the target device (will only work, if the driver itself = the *.SYS file supports the device and the OS!):
Run the Control Panel and set a “Restore Point” (as precaution measure in case of an unbootable OS).
Run the Device Manager and expand the related section (here: “Graphic Cards”).
Right-click onto the device, whose driver you want to change/update.
Choose the options “Update driver” > “Browse my computer” > Let me pick…"
Press the “Have Disk” button and navigate to the desired driver files.
Press “OK” and disregard the warning you will get.
If you are lucky, the related device will work flawlessly with your offered WHQL certified driver and will show it within the Device Manager as being digitally signed by Microsoft.