My G750JZ has started switching off because the CPU hits 80 degrees C, I've already cleaned and checked the fan so I think this will have to be the next step. Thank you for posting this!
Regarding your original question of why the fans are running at 100%, you should also check that the fan is not full of dust. This was the reason for my ROG G750 sounding like a vacuum cleaner whenever I switched it on:After a good hoover it went bac...