Computer reboots a few seconds after launching the game.

[LordHector]

In my experience, there's basically two common causes for instant reboots of a machine.

-- Insufficient power (power supply can't sustain load)
-- A very fast bluescreen (when Windows is configured to automatically reset on failure)

Try this:
Start > Control Panel > System > Advanced System Settings (left pane) > Startup and Recovery Settings > uncheck "Automatically Restart"


*If you still have instant resets on loading FFXIV:ARR, then I'd suggest trying to run Prime95 with inplace FFT's at the same time as Unigine Heaven (at max res, tessellation maxed, etc). If it's power related, most likely Unigine + Prime95 concurrently will cause the machine to instant reset too.

(these are two great stability testing tools in that they cause very-high load / will get your machine close to its limits on power consumption)

For your reference:
http://www.mersenne.org/freesoft/
http://unigine.com/products/heaven/


It'd also be helpful to know the make and model of the supply you're running.

--Essentially I'm not convinced that it's not a PSU issue, unless you've run some max-stress tests of that machine already (beyond what most games will do).

Seems like you're on to something! Unigine Heaven alone at max settings causes the computer to reboot almost instantly. (With Automatically Restart unchecked.) PSU should be able to handle it, I think, but of course it could be faulty.. Corsair TX850W btw.