Try verifying your installation. This will let the Social Club launcher (or Steam, for Steam versions) verify all game files and re-download any that are corrupt or missing.
For the standalone, Rockstar Warehouse version:
Hit "Start", "Run", and type "cmd" without the quotes. Hit enter.
Type "cd c:\Program Files\Rockstar Games\Grand Theft Auto V" without the quotes in the cmd window that pops up. Hit enter.
Note: If you’ve installed the game to a different directory, enter that directory instead.
Type "GTAVLauncher.exe -verify" in this window (no quotes again) and hit enter.
For the Steam version:
Right click the game in the “Library” tab.
Click “Properties”.
Click the “Local Files” tab.
Click “Verify integrity of game cache…”
Also
Check your “launcher.log” file located in “My Documents\Rockstar Games\GTA V”. There are helpful errors there that may give more information to assist you in resolving the problem. You can search the Support Site for specific info in that file.