This could become technical. Also, when last did you do a defrag on your hardrive? Then, you could also have a virus/worm/trojan causing instability. Especially since it is a dll issue. Do you connect to the internet with the computer in question?
Mach3 has done the same with me, but that's because I was editing a macro which was running in the background.
A suggestion, disconnect the parallel port and simulate the program, check if the crashes still happen. You could also check the CPU load. What is the CPU load while you are running Mach3?
Whacko