Check and/or swap out the printer cable, or at least plug/unplug it.
If the new computer has never successfully run your machine, I'd suspect a problem there next. Maybe a bad serial port, misconfigured, something like that. Anything you can do to swap out major subsystems would be worth a check. Another thought- Tormach had a specific list of motherboards/processors that would run the 1100 with Mach3- are you using one of those? As I recall, there were some obscure system clock problems.
Then try reinstalling Mach, or everything, from scratch.
A few years ago my copy of Mach running under XP just went nuts. Mostly, it was a spindle problem, but other stuff too. I'd reinstall, it'd work for a while, then blow up. Happened with two totally different computers (same XP and Mach images, though). I switched to PP, problem went away. Zero changes to the machine, cables, etc.