URGENTLY PLS HELP GTA4

Hi , i am having pc of specification is :

intel core] 2 quad pro
2.66 ghz
2.00 gb] ram
5670 hd radaon graphic card
WINDOWS XP ...SERVICE PACK 3

i am having problem is wheneve i click on gta 4 laucher icon ......it starts but my monitor goes blank and i am able to hear only voice not video ..... pls] helpppppppppppppppp me .....pls pls pls i am sick n tired of it ......pls nayone tell me the solution i will be really greatfull