Many thanks for all the assistance, I have got the machine running again. To sumarise: a new computer was used, blank hard drive, new XP Pro, Ver 3.04 was loaded with driver, NO JOY!! The only thing that has remained common was the XML file there definitely appear to be glitches in Ver 3.04 E.G. changing between G20 and G21 does not change the units on the screen but the units have in fact changed. I deleted Ver 3.04 and removed all of the directory contents this allowed me to put back Ver 1.84 which runs fine.
I am busy putting together a large gantry router, guess which version Mach I will be using.
Brian