Need help with unknown bottle neck.

Operating System
Microsoft Windows 7 Ultimate 64-bit
CPU
Intel Core 2 Quad Q9550 @ 2.83GHz 39 °C
Yorkfield 45nm Technology
RAM
4.00 GB Dual-Channel DDR2 @ 398MHz (6-6-6-18)
Motherboard
ECS G31T-M (CPU 1) 30 °C
Graphics
Acer X193W (1440x900@60Hz)
NVIDIA GeForce GT 610
Hard Drives
699GB Seagate ST3750640AS ATA Device (SATA) 26 °C
Optical Drives
PIONEER DVD-RW DVR-216D ATA Device
Audio
High Definition Audio Device
Here are the specs of my pc when i play Gta 4 it gives me 14fps on lowest setting and plays blk ops2 on 30fps i dont get whats bottlenecking my system?