Ok, having issues booting two different PCIe cards. XFX R7 240 and GTX 750. Documentation with DG43GT says it should automatically switch to PCIe graphics and that no BIOS changes should be necessary. I recently flashed bios to version 0035. Took it to a local repair shop and he got the X16 slot to boot with an 'older EVGA card' - (he didn't recall the model), and then tested one of my cards and says it is faulty(I don't think that is the case as I got it to boot in my son's PC). About the only conclusion I can draw is that the motherboard (2.0PCIe X 16) can only support 2.0 cards. Does that make sense? Any other ideas?
GLE3, please let me know if the suggestion mentioned above helped you.
As mentioned before, this looks like a matter of compatibility between the components. Although the cards are backward compatible you might still have compatibility issues, especially in your case where the motherboard is too old for the graphics cards. You can always try the suggestion mentioned above, and see what happens.
Just for the record, the DG43GT board *does* support UEFI, though Intel was still calling it EFI at that time (it was later renamed to UEFI when it became an Industry WG specification). The support in this BIOS is enabled automatically; there is no on-off control like you see in later-generation Intel BIOSs. Regardless, It is exceedingly rare that enabling UEFI will actually make any difference in the compatibility of a graphics card (this trick only worked in the few cases where the graphics cards included no support for legacy BIOS).
Your PCIe X16 cards claim backward compatibility. As you can see, that may not be the case. Your board was manufactured long before these cards were made, and know nothing about PCIe 3.0. You cannot expect the old board to be compatible with new products.
However, post # 3 in this thread may help you: