Your card will draw about 40 amps if you don't have it overclocked from your single rail which only has 62 to begin with. So if you're doing any overclocking with your video card AND the CPU you might be overloading your psu.
Is it that everything has been working fine for a long period of time (weeks?), and then it all of a sudden started happening or did you add something to your machine and shortly afterwards this started?
What are the computer components and case temps?