Turn off Full Screen will be the easiest solution.

If you want it full screen, you need to figure out what is pulling it back, it can be a number of things: UAC turned on? Anything else popping up? Trying to Alt-Tab? Clicking mouse while its opening? Multiple Monitors? Wrong Resolution Set on config?

Like most games you can run full screen and tab in and out freely and the game will not crash, XIV will crash if you load fullscreen and anything tabs out of it.