GTA 4 is running slow on PC with complete requirements

hi. i am currently playing gta 4 but it is running slow,specially while i'm on a mission. i can't find out the reason for this. my system specifications are way too better that required.
the pc requirements for gta 4:

OS: Windows Vista Service Packk 1 or Windows XP Service Pack 3
Processor: Intel Core 2 Duo 1.8Ghz or AMD Athlon X2 64 2.4 Ghz
Memory: 1.5 GB for Vista, 1 GB for XP, 16GB free hard disk space
Video Card: 256MB Nvidia 7900 or 256 MB ATI X1900

my system specifications:
OS: windows 7 professional
processor:Intel core 2 duo 2.9 GHZ
RAM:4 GB free Hard disk space: 250 GB
Video card:ATI Radeon HD 4350 1GB

please tell why this game is running slow and the solution.

Try updating your graphics driver.

Run dxdiag. Post screenshot of result

try The following :

Texture quality = medium
shadows quality = off
view distance = 25
details distance = 25
vehicle Density = 30

hope this help you to gain average fps more than 30 .

i tried it. not helping. the game's sill running slow. i applied the latest patch but still it doesnt speed up.

Try this: check for virus and malware.