Hey i seem to have a serious problem.. I bought GTA IV 3 days ago for PC, so i could use mods.. Then i installed the whole thing, and it worked (okay) for a few hours.. then it suddenly shut down and every time i try to start the game up it crashes.. well the whole "entering the game"-part is working fine, but as soon as i get to the loading screen saying "The Cousins Bellic" (first mission) it shuts down without any kind of warning or error messages.. 
I have Vista 7 and i didn't buy the game on steam. I've tried to run as administrator, run without Anti-virus program, re-installing and so on.. i tried all that i could possibly imagine.... If you guys have anything usefull for me i'd be the happiest man on earth... 

Im not really aware of my graphics nor my processor..

But i can run Battlefield 3 perfectly and most other games actually.. Please help me!

 

Sounds like a save game file issue. Go to my documents and find Rockstar Games, then find the Grand Theft Auto: IV folder and find the save game folder and delete the file that you find in there. Then re-run Gta iv and turn off autosave in settings. Hope this helps!

Do what MYPD98 said, but also download and run this:

 

Run it with admin privileges