The GPU may not display what is happening, but it IS doing all the work during the loading screen. It does sound like a heating issue (without more information, at least), so I would suggest checking that out. FF14 is /really/ horrible about heating cards too much.

That said, we can narrow down that very issue, or figure out if its another issue, if you would use the FF14 config tool post your computer specs to us, as well as a list of how your FF14 is configured. Pay particular attention to General Draw Quality, Shadows, AA, and AO - those are the ones that have the most impact on performance. Once those are all posted, we'll see what we can do to help.

Also consider, in the meantime, trying the most recent video drivers, though depending on your particular brand/model of GPU, you may have better luck with older cards.