You can try OCCT for stress testing as well.
Following what goat said, are you running overclocks on anything? If so, revert to stock. Maybe run fail safe defaults in BIOS, only changing what you need.
Have you physically cleaned it or inspected the system? Could be as simple as some shmoo getting blown where it shouldn't go. Perhaps reseat the video card, and try different PCI-E connectors.
P.S. I just had my Corsair CX600 pop on me, so there's that, lol.