If you only have "part03," the game will not work. You need all corresponding parts (e.g., part01, part02, etc.) in the same folder to extract the full game.
: Most files from this source use a standard password. If prompted, try: www.apunkagames.net apunkagames download-gta-apun-kagames-biz-part03-rar
Which (GTA Vice City, GTA 4, GTA 5, etc.) are you trying to install? If you only have "part03," the game will not work
: Download every numbered part (part01, part02, etc.) and place them in a single folder. If you only have "part03