If you are using an older version (1.0.7.0 or 1.0.8.0) or have "downgraded" your game for mods, players often use these community-verified tools: GTA IV FusionFix:
Getting GTA IV running smoothly on modern PCs can be a headache, especially with the legacy of Games for Windows Live (GFWL) and various launcher updates. If you are looking to download the LaunchGTAIV.exe or find a reliable link to get the game started, this guide covers everything from official sources to essential fixes. Where to Securely Download GTA IV download launch gta iv exe link