Just to be sure
Make sure you aren't using a crack - We don't support cracks -> Check, using the original GTA4 Steam version
Update GTA IV to 1.0.7.0 (the latest version of the game, or 1.1.2.0 for EFLC) - This sometimes fixes a wide variety of issues -> Check, GTA IV is up to date.
Make sure that you run the game as an administrator. -> Check
Make sure that your GTA IV root folder (and every subdirectory) is not set to "read-only" -> Check
Ensure that ScriptHook.dll, ScriptHookDotNet.asi and Dsound.dll OR Xlive.dll are in the GTA IV ROOT folder -> Check
Ensure that there is a folder titled 'LCPDFR' in the ROOT GTA IV folder. -> Check
Check that all the above files exist, if they do not, reinstall LCPDFR with the MANUAL installation. -> Check
Ensure that you are using up to date versions of every LCPDFR dependency and LCPDFR itself. -> Check
Install these: .Net Framework 4.5, Microsoft Visual C++ Redist 2012 -> Check
It looks as if it is just as it should be.