FPS Drops Fullscreen

[SzechuanMcnuggetSauce123]

So I've had my PC for months now and I noticed whenever I try to play a game in fullscreen I always get FPS drops/spikes. For an example we'll take Overwatch. before this whole thing happened I could play overwatch at 2560x1080 ultra settings with 90+ FPS but now for some reason the game just gets a lag spike about every 10 seconds causing the game to go down to about 10-20 FPS about 2-3 seconds. This whole thing happened when I downloaded a weird file for some reason and I got my PC infected (How dumb can I be right?) so I gave the PC to someone that fixed it, so it shouldnt be caused by mallware right? I've also checked to see if my CPU was throttling, but it wasn't. I hope all of you can help me with this problem and specs are down below.

GPU: Msi GTX 1070 Gaming X
CPU: i5-4460 3.20Ghz
Ram: 16gb Corsair Vengeance
Motherboard: Msi Z97 Gaming 5
CPU Cooler: Deepcool Captain 360

 

[Lakken]

Use MSI afterburner. Run it when you play games and see what happens when your fps goes down.

this was how I experienced almost the same as you and My fix
https://www.youtube.com/watch?v=wdYQJKW_WTQ

 

[Carnaxus]

Did you recently get the Creators update? Make sure you're in Game mode; they made it default to a "balanced" mode or something, and it kills games.