HARDWARE INSTALLATION
6  Two GeForce graphic cards (2-way SLI):
a) Install the second GeForce card into the outer most PCI Express 
x16 slot on the motherboard. 
b) Connect the two cards together using the dual SLI bridge 
connector that came with your SLI-ready motherboard. 
7  Connect one 6-pin PCI Express auxiliary power connector coming 
from the computer power supply to the connector on the top edge of 
the GeForce GTS 450 graphics card.
8  Reinstall the cover on your computer and reconnect any cables  
that you removed earlier in the installation.
From power supply
SLI