Bob, not had a chance to look at it further yet, pesky work keeps getting in the way, my computer doesn't shut down though, mach3 freezes or seems slow to respond.
If your computer is shutting down then that could well be an overheating problem, first thing to do is take the side panel off & give the inside of the case a good clean, you would be surprised just how much dirt & dust they suck in over time. Make sure you also clean between the fins of any heatsinks. Leave the side panel off & start it up, check all the fans are running. Is this a new set up or a problem that has started on a machine that was previously been running OK Bob ?
Thanks for the replies people, don't think it's processor problem but will check the HDD, will also run a memory test to make sure its not caused by failing memory, computer has a dedicated graphics card & everything has been fine for a couple of years but will turn off display just as a quick check.