Are you using a pirate copy of Civ V or not? 'Cause some pirate versions won't launch, even with the updated cracked Launcher.exe and CivilizationV.exe. If not:
-Try updating your game to the most recent version(a patch has been released recently);
-If you're using a third-party program to alter the in-game memory values, that may be causing the game not to launch(own experience... used a trainer once to cheat^^);
-Graphical issue... 2 possible solutions(that I know of) are a) Update your GPU drivers; b) Sometimes my graphics card just gets too hot, but when I restart comp I'm able to launch the game again. Try it;
-Deleting your "cache" folder may solve it as well(\My Documents\My Games\Sid Meier's Civilization 5\cache);
-Try launching the game directly from the game folder -- just double-click CivilizationV.exe(DX9/10) or CivilizationV_DX11(DX11).
Hope it helps.