Thank you for your post.
If the light is not going out then it is not making contact with the unit at all.
Try selecting all the available LPT ports. Try LPT1, LPT2 and LPT3 to see if any these give readings. This is because Windows can virtualise the parallel port and it could be going by a different number.
If this doesn't help, then check and make sure that nothing else is installed to the parallel port. Printers, scanners and zip drives can all cause driver conflicts. If there is anything installed try assigning it to a different port or uninstalling it and see if this helps.
Also check the parallel port settings in the BIOS of the computer. It should be set to one of the following modes:
SPP, Normal, Output Only, Unidirectional
It should not be set to ECP, EPP or Bidirectional.
The inf file is not normally visible - it is in a hidden folder. It should reside in C:\Windows\inf and is called picopp.inf. You will need to turn the invisible folders on to see this.
Let me know how you get on.