I'm not sure, I just play it off steam. Should I try and launch it with a 32/64 bit version?
Try that and if that doesn't work go to this
Program files>Steam>Steamapps>Common>Grand theft auto IV>GTAIV> And in the GTAIV folder there is a GTAIV.exe, launch it in compaitability mode with Windows XP 32 bit and try that. (It might be launch something.exe, I don't use steam for GTA)
Oh you're running 64
I had this problem to, I did what I said in up in this post and it fixed for me.