You got great hardware and that psu is excellent, its really strange.
Have tried to remove all the nvidia display drivers and do a clean install of the latest drivers from the Nvidia website?
By the way , are they both 1GB 560ti's?
Hmm, I haven't tried a clean install but they both are 1024MB 560ti's, How would I go about doing a 'clean' install? I know there are a few ways. Bearing in mind I'm running on 1 GPU at the moment. Do I need both to do a clean install?
Actually if this is to do with RAM, I do have 4 sticks of RAM in my MOBO and I set the MHz to 1600 in the BIOS because 2 sticks are 1600MHz and the other 2 are 1333MHz, I could try to take the 2 sticks of 1333MHz out set the Mhz frequency to Auto and see what that does?