|I only found 2 Corsair 750W PSUs. Both have 62A @+12V. I doubt your issue is with the PSU. |
See Pg. 34 of your user manual to learn the proper BIOS settings and which series of both AMD and nivida cards are supported.
Doesn't appear to support your second card.
Nvidia: GF 4xx/5xx series
Note: PCIe 16 #1 slot is closest to the CPU.
The BIOS has settings for each of the 2 graphics slots. Auto, enable, disable.