What do you have your settings at?

I've had the same problem, where my PC would restart itself but only in FFXIV. I had my graphics set to maximum except for shadows, which I lowered a bit because it caused a little bit of lag in the Shroud, then I tried lowering them all the way but that seemed to just delay the problem. I know it sounds weird and totally backwards, but if I set my graphics to maximum and don't adjust anything (leaving shadows maxed, as well) I don't reset outside of dungeons. Inside of dungeons on max, however, I still reset but if I turn everything down all the way I don't have a problem. I tried literally everything I could think of short of buying new hardware and this is the only thing that worked, as little sense as that makes.

Forgot to add that before I maxed my settings I would restart anywhere from as soon as I logged in to every 20 minutes or so. Since I maxed my settings I've gone a couple of days without an incident.