I've tried my RX 460s on two prebuilt computers, a Lenovo and a HP running Sandy Bridge CPUs.
I bought two Sapphire RX 460 2GB single-fan editions and neither of the two computers want to boot, but the fans are spinning. Is this a known issue? I've tried both GPUs in other systems and it works just fine, and I know it's not a PSU issue.
There's only one way for a CPU to be incompatible with a GPU, and that's if none of the motherboards that support that CPU have the right type of interface for the GPU. All RX 460s are PCIe, and all motherboards since 2009 use PCIe. Sandy Bridge is from 2011. Since they work in other PCs, it has to be either a PSU or a motherboard issue. Either the PSU can't provide enough power, or there's something wrong with the PCIe slot and either the power isn't getting from the PSU to the GPU or the GPU can't properly communicate with the CPU.
Yes there's a known issue with some of these AMD RX cards not working with a PC that has a legacy, aka non-UEFI BIOS.
At the least, you need to update the BIOS on your Sandy Bridge era motherboard and make sure the Legacy mode is turned off in the BIOS. Then it may work.
Probably the best thing you can do is use Google to see if there's a specific issue with your card. I do know some Sapphire RX 480 Nitro cards had problems with an older BIOS.
If you can return the cards, that would be Golden. I wouldn't recommend Crossfiring two RX 460 cards to anybody. Even if I didn't like them I still wouldn't recommend that Graphics card setup. You would be *MUCH* better off with a single RX 480.
Don't know anything about known issues but i have a rx470 running on sandy bridge no problems
Yes.