Sadly this problem recurred though in a different form.
PC locked up and when restarted it wouldn't go into Vista but ok in safe mode as before but this time the display was showing random shapes and signs as well as the normal display in safe mode.
Turns out it was a graphics card defect and cured when that was replaced. Search on the net turned up several instances of the same graphics card going after three years and my PC is just coming up to its.......third year...