Surprisingly, it is a windows based programme - that's been checked by the tech guy and given the all clear - it's definitely a physical/mechanical problem. Overheating could well be the reason - all tills are operational for the same length of time, yet this is the only one which freezes up. I've checked the ventilation, and there's no obstructions, however, it does have a high usage.

It reboots ok, it's just difficult to nigh on impossible to get signed in using the touch screen. The only thing I've not tried so far is attaching a mouse to see if that would help....