Well,this has nothing to do with toribash but I don't have any other forum to ask this question.

I once had gta iv on my laptop.Ran smooth with a lot of settings on high.
after fixing my laptop's broken hard disk,I decided to get gta iv back.when i run it,it was lagging unusually.I use to have around 30 - 60 fps but now I have like 15 - 25 fps on all low.What would be the problem here?I know that the game is a horrible port but it used to run smoothly.

Here are my specs:

CPU:Intel i7 3650QM
RAM:8GB
GRAPHICS:Nvidia Geforce GT 650M

I guess those are the important ones.
So please help me.

Now, I'm gonna just jump out and say it, have you asked google?

Yes.I am not that dumb.I used different types of questions and none of the links shown by google had the same problem as mine.

As you say you're using laptop... They usually have power saving modes. Make sure it's set to maximum performance.

Usually you get there by clicking battery icon near clock on lower right. (if you're on Windows)

drivers?...

all of them are up to date.
If you were asking something else,can you please extend your question?

u just answered all i asked.

did u look if u have something running in the background while playing? that eats up much space from your laptop? (other games, browser etc. etc.)

You could ask the gta community, They might know more.

Go to the NVidia control panel, manage 3d setting, program settings. Add in your gta 4 and make sure it's set to use the high performance graphics. If you need help in doing this just follow this guide and instead of toribash, use gta.
http://forum.toribash.com/showthread.php?t=358851

Hope this solves your issue.

Well,I've given 50% hope for this game but I'll try give the gta forums a try.
For all the other solutions,I think I tried all of them but thanks for the help guys.
Probably going to help me in the future.