Really good pc very unstable fps

I feel like everyday I open valorant and my framerate just gets worse, I used to get 600 to 400 fps in comp now i get 400 - 200 It just doesn't make sense. and in TDM I literally can go down to 100 fps sometimes. I've reinstalled windows, reinstalled valorant, reinstalled graphics drivers completely. I've literally done everything I can and Im at the point where I'm about to just get a new CPU