Hi,
Mach's parallel port driver has always been a bit 'iffy' on certain PCs.
Some PC's seem to do a good job whereas another very similar machine does not.
Your PC is not a laptop is it? The power saving features can really screw up a parallel port, some people have had good results
with laptops but most bomb out with them.
Have you considered an external motion controller like a SmoothStepper or a UC300?
An external motion controller removes the responsibility of generating fast accurately timed pulse streams form
the PC's CPU (where Mach's parallel port driver lives) to the external board. The external board has electronic
circuits made for the purpose and produce pulses much faster and more accurately than a parallel port ever will.
With an external controller you can use just about any PC you like, laptop, 64 bit OS, Windows 10 etc.
The downside of an external controller is cost. The two I have mentioned are in the range of $150-$200US. Note there
are cheap Chinese made controllers and Chinese made rip-offs of name brand controllers but don't go there, they are
rubbish and will cause more frustration than the parallel port.
Craig