Thanks for the response, if you turn the monitor off for 5 mins and turn it back on it works fine, it is only when windows switches the screen off after 15 mins it causes the problem.
Trying another monitor would be my first port of call, but i don't have another one available, I was thinking of buying another to try out, but wanted to see if anyone by chance had encountered this problem before.
Could it be the fan profile ? I can try that, although I have CPUID HW monitor running and the graphic card never seems to get very hot according to that, it runs at 31C on tickover.
CPUID has never been very accurate for me (used to show my 12Volt rail at 8Volts, even though the PC was running and I was gaming on it.). Try HWInfo64, seems more accurate. The temp sensor on the video card may never display or indicate the temperature of a single small part of the card that might be getting to warm: So setting a fan profile that starts spinning up the GPU fan at a lower temp might help.
While you are figuring out how to swap monitors (at least temporarily), you might also try a complete uninstall of your video card drivers and software, then reinstall all the latest drivers. It isn't often, but over the years I have had drivers so messed up that I had to do this and even go into regedit and remove everything I could find that was associated with my video drivers.
Keep us posted, please.