You need a multimeter ideally.
First check.
End to end on your parallel cable for continuity and that the pin numbers end to end all match.

If that checks out then next check.
Get the bob with nothing connected except for the parallel cable and 5v power.
Put -negative meter terminal onto bob board pc-GND pin.
Then use the +positive terminal on the output pins.
Test each pin one by one by setting it as an output for M8 coolant relay in Mach3 outputs and relay on spindle page.

So start with say P2. Set output# as P2, set spindle M8 relay as selected output#. Put positive probe on P2, (neg to pc GND). Now M8 on/off toggle in Mach3 will show either 5v or 0v on the meter if bob output Pin is working properly.
Just change selected Mach output P number as you go along.

If bob Pin not working it will either show 0v or 5v permanent regardless of on/off toggle.

If parallel cable checked OK then output fault is either bob or pc port itself. If both bob's do the sane it's the pc port.