I remember well a lecture that I attended about 25 years ago introducing the subject of Open Systems Architecture. Now I realize that the parallel/USB cable could be the fault, but this is a low probability failure mode. When I look at Printer Properties/Ports I note that USB001 has been assigned, and that USB001/HP LaserJet 3050 PCL5 appears in the Ports list TWICE! This is precisely what 'HP Universal Printer PCL6' was doing when it had hung the print spooler. Sending a Print Test Page does not print anything, nor does it cause an error message. Then I reinstalled the printer 'HP LaserJet 3050 PCL5'. After this, my other printers began to work.

That I could remove all experimental printers and print drivers. It wasn't until I came across this in an internet search: The 'hung' spooler was also causing lights to flash on my HP Deskjet D4360. I had tried installing and using so many print drivers that I had 'hung' the print spooler - Windows prevented me from deleting printer 'HP Universal Printer PCL6' and its driver.