I'm running a new machine with 2 overclocked ASUS 1GB GTX 460s. (these ones)
When I switched the machine on this morning, one of the graphics card fans immediately went to max, and there was no output to the screen. It was definitely a graphics issue, as I could hear Windows start up sound. When I rebooted, there was no problem.
This afternoon, whilst playing SC2, same thing happened twice - screen goes black, can still hear sound in the background, had to reboot.
As a test I've disabled SLI and switched the monitor to the other card, and have yet to run into the same issue.
Has anyone seen this before? Don't think it can be heat/driver related given that it has happened pre-Windows immediately on machine start up.