Are you on Windows 10? i have a CX-3 in mine now. I actually used my Win10 to crossflash all 3 CX-3 cards. The weirdest issue I had was after each boot of the first card the computer would green screen. I'd let it finish then power it off and back on and it booted fine after that. I used it to flash my 6012 in IB too. You can download the windows drivers on their website.
But you can't get your mobo to post at all? Try a different PCI-E slot?
But you can't get your mobo to post at all? Try a different PCI-E slot?