Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

We would like to recommend several troubleshooting steps:

1) Make sure that your hardware is not overheating and remove any overclocks you may have on your graphics card or processor. Please check that any fans or vents are clear of blocks.
2) Disable any additional programs that could cause interference with the game itself including chat programs. Also, remove any custom configurations made using graphics driver-level programs.
3) Turn off Fullscreen Optimizations. Find the executable file for the game (normally found in the install folder), right-click it and select 'Properties'. Under the 'Compatibility' tab, check the box labeled 'Disable Fullscreen Optimizations', then click 'Apply'.

Unfortunately, the description of the issue does lean toward a hardware issue rather than an issue with FINAL FANTASY XIV. As such, we would recommend using different a different monitor and see if the issue persists there.

Thank you for visiting the Final Fantasy XIV Technical Support Forums.