Thank you for your reply,
No, neither unit has any overclocking.
No the fault continues when performing a clean boot on both PC's, in both cases i was able to log in but the second i enlarged the window it crashed both units.
I have continued to research the fault and many articles point to it being a power supply issue, however this raises issues as the fault only appeared after performing the ffxiv update on each PC, each PC was also updated at a different times. The chances of two power supplies failing within a week of each other is slim, my partners no longer plays ffxiv and only keeps a copy on her PC for my use. We are sourcing a new Power supply to test this possibility.