Something is wrong with my new build

[KaiZo]

i5 2400
Asus P8Z68-V
MSI N560 Twin Frozr II
Silverstone 600W
WD 1TB 64mb
4GB Corsair 1333 (2GBx2)

Problems:

1 - Played Crysis 2 on 1280x1024 on hardcore setting, V-sync on - not smooth, can't tell the fps coz didn't installed FRAPS yet. What's annoyed me is that theres some kind of hang (the game stops) in 4-5min for 5sec, then returns to normal, then hang again after 4-5min.

2 - Installed The Witcher 2, can't even access the menu since it lags badly at intro. Lowest setting.

This doesn't make any sense. I can accept it if I was running at 1920x1080 but at 1080x1024 with lags? I mean come on..

Please help me. Nvidia driver is up to date (280.24) and also for other drivers.

Oh and Dirt 3 opened not in fullscreen. I'm frustrated.

EDIT 1: Pressed Alt+ENTER for fullscreen for Dirt 3, did some benchmark, got avg 79 fps with v-sync on and 8x anti something

EDIT 2: Installed FRAPS, tested on Assasins Creed Brotherhood. All high except V-sync off and anti alliasing off. Cutscreen 20-30 fps, playing at 20-120 fps, not stable. Not smooth

 

[KaiZo]

Restarted my computer, solved the lag and played at stable fps. Wither 2 still unplayable though.

 

[KaiZo]

Problem solved, played all game on highest setting.