I flashed this low power 29mh/s bios https://forum.ethereum.org/discussion/10500/xfx-rx-480-gtr-8gb-black-edition-bios-low-power-29-mh-s/p1 using atiwinflash without any problem. Make sure only one card is plugged directly into pci-x slot and not pci-x usb power riser! Also try running atiwinflash as administrator