Screen turns black after starting the game!

Hello.

For the last 10days or so, sometimes when i start FFXIV it starts just like normal but after 1 minute or 2, everything slows down until the screen turns black and I need to turn of my computer manualy. This happened maybe 1 out of 4 times when I started the game.As of today this is happening every time I start the game, so I can't play. Anyone have any ideas how to fix this?

I'm running Windows 7 with a GeForce GTX 660 with the latest drivers.

Edit: If it matters, after the screen turns black I can hear my computer starting to work like crazy, and I need to shut it down.

What do you mean by everything slows down?

The game start to lag like hell for maybe 10seconds, then my screen turns back and I need to restart my computer.