You don't need a BIOS update to support a card...
Why not keep the XFX in there and put the GIBAYTE card where that one came from?
Are these cards identical, as in same PCB and clock speeds?
What do you mean by not working? Do you get any output to screen, like until Windows loads or do you not even see the POST screen?
Have you tried a different output on the card, or another cable?