Hi, I've been running a CNC router with Mach 3 for a number of years with relatively few problems. (Finding a PC that runs XP was tricky!) It has now developed an issue with the Kress router spindle turning on. I get the message pwm bumped into minimum setting. I've had this occasionally over the years - Normally a quick 'off/on' reset will sort it out. I get an amber link light on the 'CNC Super box' controller.
I can get the spindle to come on, if I go into 'ports and pins' - Motor outputs and untick the Spindle 'step low active' button, so assume it's not a mechanical problem with the spindle motor or fuse gone.  It will not come on with the spindle F5 button, or if I try to run a program.
I tried using an old back up XML file, but still same issue.
Any help appreciated. I have attached the XML file and a couple of pics.
Thanks Dan

You might want to check your PC parallel port signals with a scope or meter to make sure they are still activating and test the relevant optocopler on your breakout board if your system is very old.

The optocouplers are usually the small ICs, often 4-pin, that are arranged in a row near the in/out ports on your breakout board. The LEDs inside these chips can fail, resulting in a signal not firing.
If your board is old, and these ICs are through-hole components, they can be easily replaced with ones purchased from an electronics retailer, with only beginner soldering skill required.
If signals that should appear on your parallel port, do not appear, then it is likely your computer motherboard needs replacing.
I'd suggest a refurbished Win XP or Win7 box rather than searching for legacy motherboards.