MY PC slows down when its not active for like 5min?!

[Domo]

Ahoy da mates.

My english is not the best so I try to keep it short.

So I turned all energy saving / screensaver off, but my screen still goes black if my PC is not activ used for longer than 5min.
I dont really mind the black screen but when I start using my PC again after the black-screen happens some of my games (including EQ) starting to get mini freezes.

Does anyone have any idea what I should be looking for to fix it?

I checked multiple times if my Screensaver or Energy-saving-mode is actived but its not :/