If it wasn't feeding the graphics card properly. You can check if your psu is working OK by downloading and running hwinfo. If the readinsgs for 12V, 5V or 3.3V are more than 0.2V from target, then you should replace the psu. Preferably with something from Tier One - http://www.tomshardware.com/answers/id-1804779/power-supply-unit-tier-list.html#13224310
But if it was me, I'd try another graphics card.