Some users experience a long black screen before the logo/menu for Dawntrail on their first-time execution of the game. FFXIV is trying to compile shaders so it is best to leave it. 

But having said that, be sure to update your Nvidia driver:

Or use DDU to uninstall your driver prior:

The shader compilation is an intensive process, so some system may throttle under this load. Laptops may take up to 10mins for this process.