Ok so I got my other 8800 GT today and installed it expecting it to blow my mind ! but instead its just gave me a headache... With SLI enabled my computer is actually slower than it was before with just one 8800GT. I've looked on the internet to see why this would happen, surprisingly there's only a few cases I could find and there weren't any definitive answers... some say its the lack of power but it seems to be on and working fine, some say its because the GPU is below 3 GHz... I tried updating the graphics card driver's no good... tried restarting(no go) ... tried crying and rolling on the floor, it looked like it worked but it turned out to be a tear in my eye.  
 
My computer specs are:
 
XPS 720 Black  Intel® Core™2 Q6600 Quad-Core (8MB L2 cache, 2.4GHz,1066 FSB) English
 
Memory  4GB Dual Channel DDR2 SDRAM at 800MHz- 4DIMMs
 
Video Cards  512MB nVidia® GeForce® 8800 GT
 
Hard Drive  320GB - Seagate 7200RPM, SATA 3.0Gb/s, 16MB Cache
 
Operating System  Genuine Windows Vista® Home Premium  
 
 
Dxdiag with one card:
 
Memory: 3068MB RAM
          Page File: 1586MB used, 4733MB available
        Windows Dir: C:\Windows
    DirectX Version: DirectX 10
DX Setup Parameters: Not found
     DxDiag Version: 6.00.6000.16386 32bit Unicode
---------------
Display Devices
---------------
        Card name: NVIDIA GeForce 8800 GT
     Manufacturer: NVIDIA
        Chip type: GeForce 8800 GT
         DAC type: Integrated RAMDAC
       Device Key: Enum\PCI\VEN_10DE&DEV_0611&SUBSYS_053C10DE&REV_A2
   Display Memory: 1756 MB
 Dedicated Memory: 477 MB
    Shared Memory: 1278 MB
 
 
Dxdiag with 2 in SLI:  
 
    Memory: 2812MB RAM
          Page File: 1129MB used, 4685MB available
        Windows Dir: C:\Windows
    DirectX Version: DirectX 10
DX Setup Parameters: Not found
     DxDiag Version: 6.00.6000.16386 32bit Unicode
-----------------
Display Devices
---------------
        Card name: NVIDIA GeForce 8800 GT
     Manufacturer: NVIDIA
        Chip type: GeForce 8800 GT
         DAC type: Integrated RAMDAC
       Device Key: Enum\PCI\VEN_10DE&DEV_0611&SUBSYS_053C10DE&REV_A2
   Display Memory: 1630 MB
 Dedicated Memory: 479 MB
    Shared Memory: 1150 MB
 
Thanks for reading.

Did you turn SLI on and do you have SP1 for Vista install?

I was just about to ask the same things.  Your version of DX10 is older than mine (6.00.6001.18000) which leads me to believe you haven't installed all the updates.  Also you have to go into the Nvidia Control Panel and enable SLI.  One last thing, download GPUZ to see if SLI is enabled also you can turn on the SLI visualization in Nvidia Control Panel to see how much and if the two cards are working.

ok I know SLI is enabled, but the Nvidia Control panel wont let me visualize it... alot of the option I should have arnt there and I dont know why... I used GPUz and I took some screenshots.... but the cards are almost exactly the same except for a few things (not thier GPUs mind you... they wouldnt work otherwise)..... and their drivers are up to date ( I still cant find the update for DX10 you have though...)
 
here's the shots  
 

put the slower one in the primary slot aswell, so that I wouldnt risk overclocking .....

Do you have Service Pack 1 for Vista install?

Just would like to make sure what do you mean for slower? Is the FPS for gaming lower? Or the 3DMark06 lower?

I always put the faster card in the primary slot, it should not throttle down but the slower card will try to keep up. But that was with 7900GT's and XP, Fista is an unknown beast to me.

 
yes I do.  
 
"Just would like to make sure what do you mean for slower? Is the FPS for gaming lower? Or the 3DMark06 lower?"
 
the XFX card has higher GPU clock, memory, and shader... that's what I mean by higher. So that's the card I dont put in my primary slot when in SLI
 
But I came across a new sypmtom, when I put the XFX card in the primary slot ( just it not in SLI) the computer doesnt recognize it... like requires me to reinstall the driver.... does this mean the computer isnt fully recognising it when its in SLI with the other 8800gt? ... hmm I might reinstall the driver with just the XFX in and then put it in SLI to see if it works... does that sound logical ?

Install XFX card only > re-install drivers > reboot, let card be recognised > shutdown and power off > install slower card into secondary slot (not forgetting the SLI bridge) and boot up > let card be recognised then enable Sli in Nvidia control panel > then enable Sli visual indicators > run 3d '06. That is the sequence I would try.

 
I did everything except run 3d '06 (im downloading it right now)
 
and I'm still getting the same dxdiag that I was when the slower card was in the primary slot... somthing is screwed up! I wish there was a switch i could hit to make it work !
 
 

jsut found a dude with the same problem, gonna try his fix
 
"For the past week my sli has been running bad worse that a single card, Both cards worked fine by themself in both slots,
I have a new Asus Crosshair motherboard but I've heard others here with differn't boards having this problem too.
After the 3rd time talking to a Asus tech I talked to a level 2 tech.
 
What you have to do is take off the SLI connector uninstall the videocard drivers reinstall the motherboard drivers first, install the latest videocard drivers restart,enable SLI restart, it will ask for the SLI connector, shutdown put the connector back on.
It works now, I can play in SLI again"

I tried it it didnt work.... but something wierd happened, I was able to enable SLI without the bridge connected and it came up with the same specs as the SLI with the bridge... any thoughts ?

What power supply are you using. Insufficient power will lower performance.

750 watts so I should be good to go

Install SP1 and uninstall and reinstall the video drivers.  The SLI visualization I believe is in the Tools menu at the top of Nvidia Control Panel Tools>Visualizations>on