FPS DROPPING SUDDENLY

So this isnt my first time having this. I had like 2 months ago problem that my fps suddenly drop to 3 fps from 120 or something. I didnt find result so i restarted my whole pc like a new one and it did help. Now its happening again and i dont know why is this happening and i dont want to restart my pc again so if you guys know solution for this i would appreciate that.