I will double check this but I think mobo / CPU / PCI-E power plugs draw from the same 12V rail (12V1).
One test I can still perform is to connect the PCI-E to the second rail via Molex-to-PCI-E converter (I have one).
I have 4 HDs, 2 optical drives and system fans & controller on the second rail (via SATA and Molex power plugs of the PSU).
EDIT
I checked and PCI-E is on rail 1 while CPU and mobo are on rail 2.
Final test :
I disconnected all components from the PSU and tested the PSU with the Antec tester.
The PSU appears to be perfectly OK, all green LEDs illuminate on the tester.
Then I connected just mobo and PCU (both on rail 2).
I switched on the system and booting sequence initiated.
The 6600 produced a picture on the screen.
I switched off the PSU, removed the 6600 and replaced it with the 8800.
I connected the PCI-E power connector (rail 1).
I tried to switch on the system but the same fault occurred as previously.
I carried out just one more test.
I connected PCI-E power via Molex connectors (but still on the same rail 1).
The fault was still there.
I feel I cannot do much more than that as I have not got another rig to test the card with.
The rail 1 was only loaded via PCI-E and the system still could not boot up.
I am applying for RMA.
