I recently picked up a set of EVGA GTX 560 Ti's overclocked to 900MHz (2GB models) to run in SLI, but I'm now having an issue with them not being detected at Windows startup. They installed fine, but every couple of cold boots (maybe 1 in 5 so far) I'll start Windows 7 64-bit up and the screen resolution will be off (800x600). If I check Device Manager both cards are listed with the little yellow triangle and exclamation point. Installing the nvidia drivers over again results in the cards being detected fine.
I previously had a pair of PNY GTX 560's in the same system that worked fine so I'm not sure what the problem might be (long story).
EDIT: I'm using the HDMI out on the primary card, so the cards are outputting video even when they say they aren't detected.
Solved. I found a thread on the EVGA forums indicating that it was a problem with the Realtek ethernet drivers causing some sort of conflict. Rolling back the driver update from MSI on my motherboard to the Windows generic drivers solved the problem.