Update!

I might have found the reason of my FPS trouble. Since it came without much reason, and even stayed after new installing my entire windows. I was not sure if it was problems with any of the programs I had on my computer. Only a few months ago, though, I bought a cheap Gamepad to play with on Final Fantasy. It was a no brand cheap one. Since then, after while of using it, my FPS problems came across. I googled about the FPS issues in TERA, and found that people had that problem when using older or non brand Gamepads. So I unplugged mine and started the game new, until now there is no issue.

I have not tried Final Fantasy yet. I will try it with my old PS3 controller, since that usually worked fine before I bought my own off brand one. Since I'd really not wish to play without controller again. But it might be that the off brand one ate my memory during my games. That would be a reason I even could believe, yet I am not too sure yet. I will see when I manage to get my PS3 controller to work on my PC again and play Final Fantasy.