need some help optimizing the game

hello guys,
although i have quite a bit experience when it comes to pc and hardware i just cant figure this out.

i formatted my pc because there was alot of stuff on it that i didnt need anymore and i made a bit of mess with folders and files everywere so i just wanted to clean all that stuff with a new installation of windows 7 64x

but before i installed everything l4d2 had 60fps all of the time with graphics at its max and 1920x1080 resolution.

now after the format sometimes my fps drops to about 30-40 when there is alot of flames and zombies everywhere, its quite annoying, cant even max out the graphics cause i can notice even the slightest bit of fps drop, and i hate that.

my specs
windows 7 64x
amd phenom II 6x 1055t (2.8Ghz)
Asus M4A89GTD-PRO
Sapphire HD 5770 (1gb)
8GB Kingston 1333Mhz DDR3
7600RPM 500GB HDD
and a simple soundcard

ive installed every chipset driver, CCC version 11.9, Directx runtime drivers. my gpu is running at normal clock/mem speed of 1200Mhz memory and 850Mhz clock. and its about 50-60 celcius so its not heating thats causing problems. also ive updated my windows.

any idea how i can get my fps back to a constant 60fps ?
maybe i missed some drivers.

 

before format i had AA at 8x and Filtering at 16x and a constant 60fps
but now i use AA4x and Filtering 8x.

 

My FPS are also low .. Well i joined EU COOP to check up on quests and my fps were around 60, even when i looked up at the sky as if i had verticle sync on when i didn't but normally, i get around 100-150 fps and if i look up at the sky then i get 200 something so can it be because of the l4d2 update? I will test my fps on other l4d2 servers to ensure it's not something to do with MG servers config ..

EDIT: This is how i fixed mine .. Go to video settings, turn verticle sync on to tripple buffer, save the settings .. That will keep your fps at 59-60 and then go back into the video settings and turn verticle sync off .. And that should do the trick .. Also, make sure that you run the game in the full screen when turning the verticle sync on because i normally run the game in windowed mode, it makes it much easier to press ALT-Tab to navigate to other things while i'm still in game ..