Silly question....do you have the 2 cards connected via an SLI bridge adapter? Pretty important step I didn't see mentioned.

 

edit:  oops, went back and read post again.  you did state you were using bridge. sorry! 

the cards just need to be the same version brand is not all that important...just don't mix overclocked and non overclocked cards...

Try the reinstall steps given

Here's another way to reinstall

http://www.dellcommunity.com/supportforums/board/message?board.id=dim_video&message.id=162466

Have you upgraded to the latest drivers?http://www.nvidia.com/Download/index.aspx?lang=en-us

 

What cards are you using?  They must the be the EXACT same brand and type to work together.

You probably can't mix a Dell brand card and an Nvidia card, that may be the problem since Dell always changes something on their brand to make it cheaper...

 

I have always used Nvidia drivers with Dell brand Nvidia cards. 

 

 

Uninstall your drivers via device manager, then dlete the drivers from your computer and empty the recycle bin. reboot into safe mode, do a drivercleaner for nividia drivers. reboot again, let windows install a generic driver, then download the latest driivers from nvidia. install those drivers and it will automatically install to both cards then it will prompt you to go to sli.  try it   madbirmy

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@Davet50 wrote:

the cards just need to be the same version brand is not all that important...just don't mix overclocked and non overclocked cards.......

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