I'm going on a guess here, and think that something is stealing focus from FFXIV in your case.
Are you playing in Windowed mode ?
Does the control come back when you click somewhere on the FFXIV window ?
If you are able to go to another program, are you able to use your keyboard there ?
Does the "Windows-Key" still do what it's supposed to do ? (bring up the Start-Menu)
We'll first need to see if these are possible, before we can look further into the problem.