Classic problem: Old motherboard, new graphics card.
Yes, the graphics card will claim backward compatibility, but in recent times this has been a hit or miss issue, mostly miss.
There is no way your board, manufactured more than seven years ago, could predict the future of graphics cards. There is no bios update that will help.
However, you should be dealing with Gigabyte, as they have the ability to modify their firmware to correct problems, if they really want to be backward compatible.
Solution, other than Gigabyte correcting their firmware, is to get a new motherboard, or a graphics card that really is compatible with your board.
Also, it makes little sense (to me) to have a seven year old board and a nice shiny new graphics card that has to operate in a degraded mode (PCIe 2.0). I would want a board that supports PCIe 3.0, so the new graphics card could perform at its best.
By the way, your processor is not supported on Windows 10;.
Unfortunately, these are the symptoms of a compatibility problem. These new graphics cards make expectations of the hardware and software/firmware that boards this old cannot meet. One requirement, for example, is support for PCIe 3.0 (your board only supports PCIe 2.0).
The problem is solved!
I have done one extra step: Reïnstall Windows 10 in Legacy mode (not UEFI).
I am glad you have the graphics card working.
This message was posted on behalf of Intel Corporation
Al Hill, N. Scott Pearson, thanks for the assistance.
I am glad to know that you were able to solve your concern.
For further questions do not hesitate to visit our Intel® Support Communities.
I am looking forward to hearing from you.