Dual non-SLI video cards in ASUS Maximus Motherboard won't boot

I have a custom built PC based upon the ASUS MAXIMUS Formula with a EVGA GeForce 8800 GT video card. Everything works great. I wanted to add a second identical video card to support four monitors. When I add the second card in, the PC will no longer boot. The external LCD Poster just says CPU INIT. The fans, disk drives, etc. do not power up. If I take the second video card back out, it boots up fine. The power supply is a 650 watt ANTEC which the box indicates that it supports dual video cards. Any idea as to what I need to do to support two video cards not linked via SLI? TIA!

Try each card individually in the system first. You know your first card works fine alone, but it doesn't work when paired with another card in non-SLI. It might help to make sure the second card works alone as well.

I updated the power supply from 650 watts to 850 watts and it now boots. Thanks!