FPS decrease without an reason

Hello! So i just played a normal game, with a balanced 70fps at all the time through the game. Well... the next game as trundle i just get in the game and i see my fps rate at 10 fps... So i get really freaked out, tried to change every setting to the lowest, only gave me up to 20 fps. Then I got the idea to restart my computer which didn't helped at all... So it cant really be my computer that's broken can it? If you have any tips or got the same problem please comment! Add on: I play Ow too, i started it, no fps changed there.