(PC desktop) The game worked great and after 3 days it gives low FPS and stuttering


I installed the game on launch and the game worked great for 3 days. Never had problems in the beta. But now the 4rth day it stutters and having very low FPS suddenly. I diddnt change anything.
I have re-installed the game and it diddnt work.
My PC Specs are: Windows 7
Msi AMD R9 280x (3GB VRam)
Intel i5 760 2.80Ghz
8GB Ram

How come the game don’t work propper anymore?