original poster, gta iv only works with certain videocards and setups with only certain drivers and certain operating systems. it is the most fickle game i have ever played. for example, i played gta iv's mission "russian revolution" with gtx 285 (+ phenom x4 780 be) and drivers somewhere around 3xx.xx or so. the game was fine until the cutscene ends and niko has to shoot his way out. the game kept doing this weird pause/freeze where i cannot move the avatar onscreen, but paper kept floating around in the warehouse, etc... swapped the card back out, put gt 640/gtx 460/gtx 465/gtx 480 and all played the mission fine.
i want you to take photos of your computer, so i can see what you are working with. otherwise i am calling bollocks on actual problem and concentrating on people who really want assistance and can follow directions so i can help