Do you have Windows PC's that randomly crash? I have seven PC's in my house running Windows, and none of them ever crash, including the one running my router.
As long as the PC is only used for running the machine, once it's setup and running properly, you shouldn't have a problem. Just disable all power management options, and don't run any antivirus software. Basically, Install Windows, then install Mach3. That's it.
If Mach3 just randomly crashed every now and then, do you thing there would be over 50,000 registered users.