You should download and install the Windows ISO on a USB Flash drive to avoid that issue and you can also apply the latest updates to that ISO as well so you don't have to install millions of Windows updates, lol. But if you have a spare drive, try that first and if you can, try installing the game on another computer, just swap the PSU and GPU and you should be able to test it. You can also try copying the game files to the other PC and it should work by just downloading the client only too.

I would honestly install Windows 10, it works great and my FFXIV game never crashes too, I can Alt/tab better than in WIndows 7 too.