Sparkle geforce 9600 GT sli problems

Hi,
i have recently upgraded to SLI graphics card, but the option to enable the sli is not available in the control panel
my system is:-
mobo: asus m2n4 sli
psu: ocz stealth x stream 700w
cpu: AMD athalon 64 bit dual core 5600 black edition
Ram: corsiar twin dominator dual channel 4gb

i have uninstalled my old graphics drivers and installed the new ones and ive even gone to the nvidia
website and downloaded the new drivers but nothing. the bridge is of course connected and the power lead is plugged into both of the cards
any help would be apprecated =]