mopman411 :
I have been looking to find info about the motherboard from the computer model you provided but I have been having difficultly finding anything that tells me the exact motherboard that you have in that computer. I hope you can provide more info about the motherboard.
Strange that Powerspec would suggest the card is not getting enough power. PCI-e 1.0 and PCI-e 3.0 provide the same power at the slot. PCI-e 2.0 is the same specs. Something that could cause what you are experiencing would be a power supply that isn't providing enough juice, I doubt you are in that situation but make sure you have a 400w PSU that is providing at least 24A on the 12v.
Just in case it might be a power issue, I replaced the PSU with a brand new Corsair TX650 650 watt and I have the same symptoms (GeForce 8800GT GPU won't load driver and ATI R7770 won't boot--just a black screen) So I guess the only remaining suspect is either the BIOS (which has no update available since 2008) or the motherboard. Is there a way to check if part of the motherboard is not functioning? I did get an overheating message before the problem appeared. The motherboard has the following components:
Intel Intel(R) 82801 PCI Bridge - 244E
Intel Intel(R) G33/G31/P35 Express Chipset PCI Express Root Port - 29C1
Intel Intel(R) G33/G31/P35 Express Chipset Processor to I/O Controller - 29C0
Intel Intel(R) G33/G31/P35/P31 Express Chipset PCI Express Root Port - 29C1
Intel PCI Simple Communications Controller
Intel PCI standard PCI-to-PCI bridge
Intel Pont ISA standard PCI
Microsoft Microsoft UAA Bus Driver for High Definition Audio
Synaptics Intel(R) ICH9 Family SMBus Controller - 2930