You are trying to use a 2019 video card on a 2012 motherboard that only supports PCIe 2.0. The card will claim backward compatibility, but, as you have discovered, it may not be.
Even if it did work, you would be running your nice, new card in a degraded mode and not experiencing its full performance.
There is no way your existing motherboard could predict the future. Get a new motherboard that supports your card, or get a card that is really backward compatible.
The PCIe support on X79 boards can be very confusing. This is compounded by inaccuracies, (I am guessing) due to over-simplification, in the DX79SI, DX79TO and DX79SR TPS.
What PCIe support you have in the x16 and x8 slots is dependent upon which processor you have installed:
- If you have a Core i7-3xxxX (i.e. SandyBridge E) processor installed, then you have PCIe 2.0 support.
- If you have a Xeon E5-2xxx (i.e. Sandybridge EP) processor installed, then you have PCIe 3.0 support.
Regardless of the processor installed, the PCIe x1 connectors, which are all supported by the X79 PCH, are all PCIe 2.0.
Bottom line, depending upon which processor you have, you could be seeing a PCIe 2.0 vs PCIe 3.0 issue.
Overall, you need to remember that, even though X79 is titled as being a 7 Series chipset, it is really just a souped up 6 Series chipset. Similarly, the Core i7 processors, even though marked as being 3rd generation processors, are really just jazzed up 2nd generation (Sandy Bridge) processors. Finally, the DX79xx boards are older products than the other 7 Series boards and thus will more than likely have compatibility issues similar to those seen with the 6 Series boards.
I missed something. There are actually two things that can cause compatibility issues, the PCIe support level and the UEFI support level. In some cases, enabling UEFI boot will overcome the compatibility issue.
Probably the card is trying to negotiate pcie speed, or just UEFI boot rom support bug. This can be related to the size of the card's option ROM. I don't know if this motherboard can boot headless,but if it can, Try the following:
-download and install DUET. DUET is an off-firmware UEFI implementation. you have 2 choices:
-turn off uefi (you have to at least have one uefi bootable OS).
-your card is UEFI based, so it won't be initialized.
-Refind will patch gop, and probably try to reinitialize your card. Because of gop enabled, motherboard will see UEFI option rom and successfully initialize card.
This will slow down the booting process +2 mins, but it should work. The tianocore implementation of UEFI is far more reliable than Intel Motherboards bios Implementation, so if this works, probably it will enhance compatibility.