A couple of basic questions come to mind as you haven't addressed them yet.
Have you checked out your power supply. While Corsair's TX series is very good and has a very good rep, it is still possible to get a bad one that be giving some flaky voltages on on the 12v rail. According to this article by Anand Tech
you should be drawing about 500-525ish watts (that's total sys load) with those cards in SLI. Do you have access to another PSU? Push come to shove you may try removing it to a local shop that can properly load test it (I'm paranoid so I would want to make sure they could in fact load the unit and didn't just use a DVM to check the voltage).
I don't have another PSU to test, but the integrated digital meter (I know, not always accurate, but my board doesn't have test points) shows the +12v as being at or above 12v at max load with furmark, prime95, or crysis.
It is important to remember that the load will fluctuate depending on where you are in your game or current endeavor. This variation can cause fluctuations in the voltage avail at the various rails. To much variation and things can get screwy. You could try to monitor this your self with some success with a program like Everest to monitor the voltage real time. You may try to do it with a DVM hooked up and watching it while you loaded up the system. But you really need be able to see what is happening as it loads and unloads to make sure the voltage regulators are doing what they should.
I'm using Everest. The +12v stays between 12.14v and 12.1v.
Have you updated the BIOS recently? As in everything was fine once upon a time, but now it's not. If not have you checked for the latest BIOS? You may read the basic descriptions of each to see if any address similar problems.
There is a new version, but all it seems to do is disable Active Phase Switching (a power-saving feature) during Overclocking. I will try it, though.
Have you confirmed that you have the latest chipset drivers for your specific motherboard.
I reinstalled Windows when I installed the new components. I was using 32-bit and wanted to use 64 to take advasntage of all 6GB. When I did, I got the latest 750a drivers from nVidia.
Have you tried completely uninstalling all nVidia software removing the cards and starting over with the drivers and software.Be sure to follow recommended procedures/use nVidia removal sftwr/rmvl tools, or something like Driver Sweeper.
I was experiencing the same issues before reinstalling Windows, when I used my components while backups were going.
I don't know about nVidia software/hardware, but part of ATI's recommended procedure is to remove their folders after uninstalling and then going to the device manager and in properties for the cards clicking on uninstall for each card. Just before doing the restart I even empty the recycle bin so Windows can't go there to reload anything. Note; Windows generic drivers are good enough to get you up and running on the restart with one card till you get their software installed.
I formatted the partition. Would you like me to try uninstalling all of it again?
If all your software (drv's and BIOS) is up to date, both cards run fine, your PSU is good to go, and you have replaced your bridge but the problem is still there, I would say the problem has to be with the mobo itself.
Thanks, that's where I'll look next, if the new bridge doesn't fix it.
EDIT: I updated the BIOS, no change.
Final Edit: Got the new SLI bridge in, it looks different, darker, and the MSI logo on it is different. I put it in and voila, problem solved. Thanks for your help, everyone!