Here is your solution.
read These steps carefully.......
1st.=Note your product key on copy or in your laptop.Then Note your unlock request code on copy or in your laptop.
2nd.=Go to this site-https://support.securom.com/rockstarunlock/GTA_IV/index.php?c=offline
3rd.=Paste or type your key and request code in empty fields.Then click on generate code.After that your unlock code will generated.
Note down your new code which u generated.
4th.=Then download this package=http://download.securom.com/support/gta4/GTAIVPC_OfflineInstaller.zip
5th final step= To complete your 'Activation', follow these steps on the computer where the game was installed (Note: You may need to make sure you have admin rights to finish this process):
Copy the 'GTAIVPC_OfflineInstaller.zip' file to your PC's desktop from your laptop.
Once copied to the desktop, double-click on this file to run it; you will be prompted to select your preferred language and to review the license agreement
Click 'Next', and the file will 'unzip' and will automatically 'download' it's contents to the proper location on your computer
Launch Grand Theft Auto IV PC (see game manual if you need instructions)
You will be prompted for the 'Unlock Code' that you obtained earlier from a PC with an Internet connection, as well as your 'Product Code' (serial number)
Enter these codes in the applicable fields and click 'Activate' to finish the process
Your game will now be fully installed and activated
So if i help you, then its my pleasure...