Problem with screen going blank

I am having a problem with my screen going blank. When I run benchmarking programs such as 3DMark05 my screen goes blank. I have no problems playing doom 3 with all of the settings turned up or while doing everyday task. The only other time I experience this proplem is when I end a video game emulator such as ZSNES which has a GUI interface. I dont think that it is a hardware issue but a software issue. I have a apple 20inch display hooked up to a SLI system and I think this is causing the problem because in order to get my apple display to work on the SLI system I need to hook up a crt monitor, then activate SLl in windows, and then restart the computer with my Apple LCD hooked up. After that SLI remains activated. This problem occurs at stock speeds so I know it is not a problem with my system being overclocked. I have tried diffrent drivers and bios but still have the same problem. ANy suggestions?

Asus A8N-SLI Delux (1007 bios)
2 MSI Nvidia 6800 cards (71.89)
FX-55 cpu
2 gigs OCZ DDR 533 platnium ram
OCZ 600w PSU