1. And you've made sure the Power Options in the Display settings isn't set to turn off the monitor in 1 minute?
2. You don't mention the operating system but it appears like this may be a driver issue.. Is it a 32 bit or 64 bit machine? Which OS? Have you checked the video card's website for the most recent driver? Or even tried an older driver which works?
3. Tried updating the BIOS?
Hope this helps.
About 1 minute after booting to the desktop the screen either turns black or grey. Not the video card (5770).
Works fine with my old video card (7900gtx)
Got a replacement 5770, no change
Tried a different PSU, no change
Different monitor, no change
Any help/suggestions would be greatly appreciated