Thanks for all these suggestions and explanations. AVG is out of there! If this does not work then I had made my mind up last night that it was time for a fresh install. That machine actually has 2 hard drives (the other one is not used but contains the old system that got too clogged up) so I am going to reformat the other one, re-install windows, any vital drivers, then mach3.

Wife is asking when she can have things engraved again, so no pressure then!

By the way, if I were to create an 8KHz square wave (of about 3-5v) and inject it into the system3 parallel port pin 3 and earth, would the stepper rotate or does it need all the other pins to be present (board has a charge pump override)? I have access to lots of signal processing kit at work and could easily do this, or even borrow a signal generator to do it live.

Thanks
Barry