I'd suggest checking the Windows Event Log to get more details on why it's crashing.

XIV is notoriously picky about how it interacts with both the Nividia drivers and Windows drivers so if things aren't perfectly aligned between the three, errors of varying severity will occur, ranging from simple client crashes to GPU/PC crashes like you're experiencing. Down/upgrading Nvidia drivers can sometimes fix it.

I started having GPU shutdowns after Windows upgraded me to version 1809, which I seem to have finally resolved by both downgrading to a known stable Nividia driver (416.94 with the latest Windows version) and also updating my motherboard chipset drivers to the latest ones as well. After doing so, I only got a minor client crash as my latest error, which I believe was tied to the Windows Game Mode being on, so I shut that off and am hoping things are finally back to normal.