Potato FPS After installing Portal 2

[KyLo_ReN]

I have installed Portal 2 and now all my games run TERRIBLY.
Specs:
i3-6100
GTX 950
Original HDD: 500GB Western Digital Green Power
Any tips will be appreciated
(I have restarted my PC and reinstalled GPU Drivers)

 

[COLGeek]

From where did you download Portal 2? Have you scanned for malware/viruses lately?