A 720w is more than enough for this card. Actual use is 180-240w max with overclocking unless you psu is defective your card is the issue. These cards tend to have such issues when they are neglected by their owners by failing to keep them as cool as possible from the start. At high temps they like to slowly degrade over time even though the vram and gpu core are just fine. Better built than the 275 and 285 but they are needy cards.