Sounds like a hardware problem to me. Have you tried reseating the graphics card? Also, post complete PC specs including CPU, RAM, Motherboard, Graphics card, HDD, SSD(if any), and especially the PSU make, model, wattage and available current on the 12v rail. It could be that your PSU is getting weak.
No I did not try to reset my graphics card as I don't know how to do that.My system specifications:
Gpu: AMD Radeon HD6870
Mb: ASUS P8H61-M LE
Psu: CM GX650W
Ram: 2x2Gb DDR3 1333mhz
HDD: Seagate Barracuda 1Tb 1000rpm. (not sure)