Pull the card again. Check the PCI Express slot for any dust or debris that may have gotten into it. Reseat the card and try again.
What PSU do you have? There's a big difference in power draw between a HD4770 and a Fermi. What is your monitor's resolution? A single HD5770 may do quite well for you.
1680x1050 screen resi
antec 550 modular psu
I had added another hdd to recently to make a raid+0 and also have alot of OCing in the puter at the moment so going to try removing 1 of the hdd's and reseting mobo back to factory settings. Computer will boot fine off onboard or with older video card in the pcie x16 slot