These Questions have most likly been ask many times so heres my stick onto the fire
 
ok first here is my set up
 
MotherBoard: GA M55sli - S4
CPU: AM2 5800 + 2.8Ghz
Sound Card: On board
Hard Drive: 500Gb
GPU: 2 x 8800GT's 1 is gigabyte 1 is generic (EliteGroup)
PSU: Coolermaster 650W
 
ok i have been trying to get this thing working for the passt week with no luck  
i have installed the 2nd card but it has not poped up in my device manager i have tried each card one at a time and they are both working  
i have reinstall the lastest drivers for both my video cards and motherboard. i think my powersupply is powerfull enof and i have checked there doesnt seem to be any setting in the bios to activate SLI and theres no switches on the motherboard itself
 
anyideas    
 
Cheers

Do you have an additional molex power plug connected to the molex power connector on your motherboard above the 1st video card and the processor? (you have to have this when you run two cards)
 
Check the bridge connector and make sure its correctly seated between the two video cards.
 
There is a setting that you go into to "enable SLI".  Go to your control panel, then Nvidia control panel and then "set SLI configuration"  and make sure SLI is enabled.  
 
I had that board and it worked great.

yep thx i pluged that in thou it didnt have any effect its still not detecting the 2nd card thx anyway