Windows running slowly

[2slow4me]

Yesterday, I installed a clean version (i formatted the partition which contained the previous Windows) of Windows 8.1 (64-bit) + updates (Legit version, got it as a student). However, after playing some games, I noticed it was running worse than when it had a Windows 7 which was gathering everything for a year and a half. 

I updated my drivers that ASUS provided, i updated my graphic card drivers, checked if the redistributables were updated (directx, dotnet, visual c++), but the games still slower (lower FPS) and in some cases, my old PC (5-6 years old) runs them better. 
 

Short specs:

ASUS x550V:

i3-3110M 2.4Ghz

4GB RAM

GT740M

 

I'm going crazy, don't know what the hell is the problem, and i can't downgrade back to Win7 cause ASUS withdrew the windows 7 drivers from their site.