I think you need a new power supply. I've heard from alot of people that had the same problem as you and the key to fixing the problem was to get a new power supply, and it worked. but they had high end video cards. I am not totally certain its the power supply but im positive. Your power supply is 12V@15A
A minimum PSU should have a minimum of +12V@18A and a 16ms hold-time
If you are getting a PSU for a system with a single high end video card than 28A-32A should give plenty of room
Midrange systems should shoot for 24A on the 12V rail
Really low-end, older or specialty systems can consider 18A on the 12V rail
Your system looks like a Midrange system so you need a power supply on the 12V@24A or higher.
Your amps on the 12V rail is 15A and lower than a low-end system witch is 18A
I suggest you get a new power supply as a last resort if you havent already solved the problem. But then again you need a better power supply anyway.