Hope you can give me some ideas on this one. Bear with me and I will try to get all the details in without boring you!
1) Attempting SLI for the first time in my system...a system which until this point, has been rock-solid stable!
2) Asus P8P67 Deluxe MoBo, Intel i5 2500k CPU, Corsair TX850 PSU, ThermalTake Frio CPU Cooler, Patriot RAM. Running Win764.
3) Graphics cards are Palit GTX570s - but very slightly different models. One is a GTX570 one is a GTX570 "Sonic". Having investigated this, even though they have different part numbers and a different BIOS number in GPU-ID, I am fairly confident the only real difference is the very small factory OC on the "Sonic" edition. Power architecture and the GPU chips should be identical.
4) With both cards installed and the SLi bridge in place, the system boots fine and will allow me to use the desktop, review and change the SLi settings etc.
5) If I try to run any benchmarks or recent 3D games, I get between 0 and 30 seconds worth of play before the screen goes black or displays some other random solid colour and then the monitor goes into power save mode and the system hangs - powered on but completely unresponsive.
6) I can use the desktop, MS Office and seemingly play 2d stuff like Terraria without any problems.
7) Card temps are around 44-46 at idle (or in 2D apps)
8) Card temps start to climb and the fans kick in as one would expect in 3D gaming, though they only seem to get to 60 or so before the system hangs anyway.
9) I have tested both cards individually in both PCIe slots with nothing in the other slot - everything works fine under both benchmarking and gaming.
10) With both cards slotted in with power connected, I get the same hanging issue even with SLi disabled and using the second card as PhysX only.
11) Although my rig originally had a 30% CPU OC, I have subsequently disabled this as part of my troubleshooting and everything is running at stock.
12) I have tried using MSI Afterburner to reduce the small factory OC of the "Sonic" edition card so it matches the stock one exactly - no joy.
13) I have used the 280.23 WHQL drivers and the latest 285 betas - no joy.
Now according to my calculations from here, my 850W PSU with 72A on the 12v should be plenty sufficient for this setup - even with the CPU OC...but the symptoms seem to indicate power problems? Any other ideas? Could it just be drivers?