So I have a custom built pc. stock Intel i5 6600k and Nvidia geforce gtx 980. Before i had around 50-60 fps on witcher 3 but after nearly 10 min of playing the game the fps drops to 10-15. i cleaned out my pc. I monitored the temperatures and everything seems to be fine. I'm not sure about voltages but i have not messed with anything. I had defragmented my harddrive, reinstalled display drivers but the problem still persists. What I really dont understand is that problem doesnt start from the beginning itself rather it presents itself after som 10-15 min. Please help