So I've had this pc for about 2 years I believe. I can't say it's the best one out there. In fact, it's quite horrid. A problem I've had which I don't suspect has to do with it though is the framerate behaiviour toribash has.

It's normal for my game to start off at a solid 60 fps on low settings but after about 5-10 minutes it starts cutting down to 30. after that, 15. Seeing as it starts off at 60, doesn't that mean that my pc should handle the game quite well? This problem has occured ever since I got the pc. I believe my last one had a similar problem aswell. Any help?

I may also note that not only does the framerate lower, but the speed of the game aswell. A simple replay would only look normal if I speed it up to 2x the speed.