This had happened to me I think it's because of your mods because if you replace most of .dff or .txd it may lead you to freeze/stuck at the loading screen.
I recommend you before inputting some skins like weapons, vehicles, roads, and etc, make sure you have a backup gta3.img so if there's a problem just copy and paste it on models replacing the old gta3.img that was trying to freeze you on loading screen.
