Trouble with Sapphire Radeon HD 7750 and Windows 8

Having trouble installing windows 8 (OEM on a clean drive) with Sapphire Radeon HD 7750. The installer originally would go to a black screen after the "preparing devices" stage, so took out the card and completed windows 8 install with the integrated graphics. Then tried to reinsert the card, but got a black screen on boot up (after the windows 8 logo). Also tried booting without the card in, installing the drivers from the amd website, reinserting the card, and then booting up, but got the same result. Finally, tried disabling the integrated graphics, as well as changing the primary video controller to all three of the following:

GFX0-GPP-IGFX-PCI
GPP-GFX0-IGFX-PCI
PCI-GFX0-GPP-IGFX

but got the same outcome. Any suggestions on how to fix this?

Thanks.


Other relevant parts:
Mobo: biostar a780l3c
CPU: AMD Athlon II X4 640 Quad Core 3.0 GHz