Maybe the DVI to VGA adaptor is bad. This must be a old monitor if it still has a vga cable. Know anyone with a DVI monitor you could try? If that doesn't work, put the old card back in and try updating your bios.
But even if the adapter was bad, that doesn't explain why the computer wouldn't boot or load up the OS. (Only when the XFX card is installed; the computer boots up fine when I take the XFX card out.)
I have a new i3 540 + dp55wb + Seventeam 650w PSU and it works perfectly with my old geforce 7600GT but won´t boot with my new XFX 5770 card. I´ve send back to seller and he said that it works perfectly for him. I don´t know what to do anymore. I´ve upgraded the MB BIOS, and nothing. Someone could help. I don´t know what to do anymore and i´ve seeing a lot of people with the same problem with others MB and CPU configuration. HEEEEELLLPPP ME PLEASE!!!