Why does gta 4 not run properly on my laptop?

Now,i bought a laptop which has very high configs. like core i7 processor,2gb graphics card,4gb RAM etc.etc.I installed gta 4 on my lappy which ran great in optimized settings.I tried to make it run on extreme settings but my laptop freezed.Also it did not run quite smoothly when i tried for a 2nd time.plz help...I do not want to run it on full settings but still,WHY DOES IT FREEZE EVEN THOUGH MY SYS CONFIG. IS QUITE HIGH???