I build my friend a computer just at the end of 2017 (before Ryzen!), with a 7600k CPU and the asus strix 1070. The first couple of days it worked perfectly, with 100+ Fps on Overwatch, but when he tried to install Rocket League, the game only ran with 1-2 Fps. The next day he couldnt even run Overwatch (0-1 Fps). I then made him check task manager at, and he said that it the CPU usage was at 100% constantly (80-90% from Overwatch, 10 or so from Discord). I then searched the webs and found only people wondering why the CPU usage was so high, but none had less than 70 Fps. The motherboard is a h270 so no overclocking (his choice).
System specs:
i5 7600K
Asus Strix 1070
Asus ROG Strix H270F Gaming
G.Skill FlareX 16 gb
Cooler Master Hyper 212 EVO
Any help would be greatly appreciated, but it may take a little time for me to response, cause i dont have the computer that close.