Go to: steamapps/Common/GTA 4/GTA IV/LCPDFR/Diagnostic's tool.
That will create a log file in the LCPDFR Folder, Then copy and paste the whole log file to this post. :)
[If you bought the game on Steam]
I start up GTA 4 But LCPDFR Wasn't working correctly, I checked the diagnostic tool, And the only thing that had an error is the LOG File.
Halp Plz
Diagnostics_27.12.2016_14_37_56.log