Ok, first off:

1) Are you using a razor mouse? If yes, skip to step 2. If no, proceed to next post.

2) Load FFXIV. Hold left click, right click and middle mouse simultaneously for 20-30sec. Does your computer shut off? If yes, you have the mystery razor mouse bug. Proceed to step 3. If no, proceed to next post.

3) There is no known fix for this issue. Purchase a new mouse. Lucky you, it's black friday.