I bought one of these http://www.amazon.co.uk/gp/product/B00N8THK8K (which is listed as UEFI compatible, requiring a 150W 8-pin power draw) to replace the stock Radeon HD 4870 that came inside my Early 2009 Mac Pro 4,1. I've read that the R9 285 is supported in recent OS X versions, but I'm not even getting as far as booting OS X or Windows from what I can tell. It fits okay, all cabled up etc, but no happy POST bong or boot of any kind. My default boot partition is actually my Windows 7 Bootcamp, so it usually boots that if there is no keyboard intervention, but nothing happens other than fans and HDDs spinning up. The HDDs are just spinning; they don't sound like they're being read during boot, so it's not that the machine is booting but I'm just not seeing anything. I realise this card is not flashed with Mac specific firmware, but the card is listed as UEFI compatible, and regardless of that, my understanding the worst would be that I would just be missing is the ability to see boot screens? Is this card simply too power hungry? Am I doing something stupid?