Sometimes, the older executable hates the modern Windows desktop environment. Right-click GTAIV.exe , go to Properties > Compatibility, and check "Run this program in compatibility mode for Windows 7." Also, try running it as Administrator.
The most reliable method currently is using an automated utility: GTA IV Downgrader (by ItsClonkAndre) downgrade gta iv to 1070
Downgrading Grand Theft Auto IV: The Complete Edition to version Sometimes, the older executable hates the modern Windows
Technical Report: Downgrading Grand Theft Auto IV to Version 1.0.7.0 Downgrading Grand Theft Auto IV (GTA IV) Reverting your files provides distinct advantages: GTA IV
The current Steam and Rockstar launcher builds (version 1.2.0.XX) present severe hurdles for enthusiasts. Reverting your files provides distinct advantages:
GTA IV was designed for dual-core CPUs. On 6+ core processors, it can stutter. Use a launcher or a simple batch file:
: An all-in-one automated tool that guides you through selecting your directory, backing up files, and choosing the 1.0.7.0 patch. Gillian's GTA IV Downgrade Utility