Quote - It lives!!!!! Well I took the casing off and cleaned out a lot of dust from the inside including the fans and so far all seems well. No problems after being on 2 hrs at the moment. Keeping my fingers crossed.

Could be an intermittent fan on the CPU or video card, which is why it wasn't working and is now working again.  In my experience when a PC shuts down completely all by itself with little or no warning, it's usually because the CPU overheated and the mobo shuts itself off as an emergency precaution.  Same thing could happen with the video card and its GPU.

The next time you have the problem, boot up with the case off and make sure the fans on the CPU and video cards are spinning.

LH