Okay so I had the same issue. Here's what I learned.

1) You cannot have any of your audio devices set above 44.1khz. (control panel -> Sounds).

2) Check third party devices. Have you plugged anything new in? ANYTHING at all? Unplug everything but your mouse and keyboard and see if it boots; then continue adding back devices until you get it working. In my case, it was my Apple Cinema Display. When that is plugged in (via USB, which is what controls the webcam, speakers, and built in USB hub. I have to unplug the USB cable to play FFXIV, video is handled by it's mini displayport cable) it won't work. Check out webcams, USB headsets, USB hubs, thumb drives, etc. Anything.

3) Steam overlay, teamviewer, teamspeak, anything that might inject code needs to be nixed. Same diagnostic process here. Close everything, fire up FFXIV, if it works; start re-opening software until you find the one that is the culprit.

Good luck! I finally got mine working again on my Windows 7 PC.