Can you tell us which operating system you have, and have you got any parallel port devices like printers, scanners etc. installed? Even though the devices might not be connected, the drivers might still load at start up. Even reinstalling windows could cure your problem. Do you get any error messages when your system crashes? Or does it just freeze? If you have XP loaded, when you get a crash, try and leave the system for a while before you reboot, sometimes the OS will recover and give you more info. Also check your BIOS settings, if you are overclocking it can be a problem. Have you got a Machine debugger running in the background? Another option is to disconnect the parallel ports and modbus if you have one, and run Mach3 in simulator mode, and check if you still have a problem.
Whacko