Gigabyte hd 7870 not compatible with a biostar A88OGZ ?

I have a Biostar A880GZ motherboard, with a 2.8 PhenomII CPU, 8GB RAM (2 4GB G.Skill RipJaws) and a modular 530w Power Supply. I bought a Gigabyte HD 7870 and it does not show image through the only possible way i have at the moment, DVI to VGA adapter. I wonder if the GPU is compatible with the biostar A880GZor if its a common problem. I'm considering updating the bios, but i'm afraid of screwing that up since i don't have experience on that matter. Other thing I'm wondering, that motherboard is 2.0 PCI and the card is 3.0, would that make them incompatible ? And for last, thinking alternatives, I'm doubtful about the 530w power supply, should i change it ?

Any help would be very much appreciated.