Sounds like you may be over stressing something and it's causing the driver to crash. If you were loading it in full screen, you can edit a text file to set it back to standard windowed mode. Or if you were in Windowed mode, you can trim the resolution settings to smaller size to see if it lets you get back in to adjust your settings. If all else fails, you can set them to default via the config button in the launcher, but I think that resets all your HUD elements too... forget.
Anyhoo... to get to the config file, open your file manager (double click computer or open the folder icon if it's pinned to your start bar). You will need to drll down this similar path:
C:\Users\<YourWindowsUserName>\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn
The file you want is FFXIV.cfg. Depending on your view settings, the .cfg may not be showing, so you may only see FFXIV. You can right-click the file and choose "Open With" to open it with any text editor--notepad will work just fine. About 15-20 lines down, there will be a section for <Display Settings>. This will list your windowed screen resolution, your full screen resolution, and then a setting for the mode. It will look something like this:
Code:
<Display Settings>
MainAdapter
ScreenLeft 142
ScreenTop 61
ScreenWidth 1600
ScreenHeight 900
ScreenMode 0
FullScreenWidth 1920
FullScreenHeight 1080
Refreshrate 60
Most of it is self explanatory for the hardware geeks, but all you really need to worry about are ScreenWidth, ScreenHeight, and ScreenMode. That will be the width and height of your window, followed by the mode of the display--the setting of 0 is for the standard windowed mode. Not sure of the exact values, but considering the order in the menu, 1 may be for borderless window and 2 for full screen. Just speculation there, but 0 is for normal windows mode. Make sure that ScreenWidth and ScreenHeight are set to valid values to fit on your monitor, then set the ScreenMode to 0 ,then save the file. It should now load in a normal window again.
You could try toggling some of the other settings manually as well. Some are obvious like a 0 to disable AntiAliasing and such... but hopefully by forcing it back to a windowed setting you will be able to get back into the menus and do it that way to be safe.