Gta 4 pc graphic problem?

pc specs: intel i7 2.2GHz (3.10 turbo) 8 cores 6gb of ram nvidia geforce gt555m 2gb so when i start the game the graphics are f-upped and most of the city is transparent. when i go on graphics menu it says that i don't have enough memory on my graphic card and that i have only 52 mb instead of the 2gb i... show more pc specs:
intel i7 2.2GHz (3.10 turbo) 8 cores
6gb of ram
nvidia geforce gt555m 2gb
so when i start the game the graphics are f-upped and most of the city is transparent. when i go on graphics menu it says that i don't have enough memory on my graphic card and that i have only 52 mb instead of the 2gb i actually have on it. i can play fu*king battlefield 3, skyrim and assassins creed revelations all on high settings and these are all recent games, but when it comes to a 5 year old game it fu*ks up. WHAT MUST I DO. CAN THIS BE FIXED????
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