My PC games are lagging for no reason! What do I do?

have core i7-3720qm, 2.60ghz, 16gb ram, , 64 bit operating system on windows 8
i'm running windows on bootcamp, on macbook pro retina display
there's problem games lagging , no logical explanation why they're doing so. week ago games run @ 1080p resolution 60fps 1 day came halt , drops 20fps , kind of lags @ 720p.
i'm running games on steam, , if switch mac , play games steam work on mac, work perfectly, tf2 exact, performs garbage on windows.

here things i've done, , feel there's nothing left
updated nvidia drivers, downloaded recent version of catalyst, made sure clear out dust computer wasn't overheating, it's not possibly hardware problem because these games work charm on mac side, don't run operating systems in parallels, know can't have memory being used! defragged everything, cleared disk space, have 50gb free on solid state drive!!

has happened once before, , magically fixed itself.... time it's taking twice long....

don't know possibly do... hell wrong windows, it's performing garbage, have high performance checked on battery preferences too.... like, what's going on!! me

i have core i7-3720qm, 2.60ghz, 16gb ram, , 64 bit operating system on windows 8 i'm running windows on bootcamp, on macbook pro retina display there's problem games lagging , no logical explanation why they're doing so. week ago games run at...

Consumer Electronics Games & Gear PC Next