Ubuntu 14.04.3 won't install HP LJ2100M printer

Symptoms:
 1. hp LaserJet 2100M printer won't print under Ubuntu 14.04.3.
        (It still works under Ubuntu 12.04 installed on a laptop
         suggesting that the printer hardware is probably OK.)
 2. Printer setup (SystemSettings; Printers; PrinterProperties)
        can't or won't find the LJ2100M. Attempts to force the
        issue by declaring a Device URI
               "USB://HP/LaserJet%202100%20Series"
        (as used on the 12.04 platform) are rejected and the system
        returns the error message:
                "Cups server error, client error not possible".
        The system then autocratically replaces the Device URI by:
                "file:///dev/nul"
        Needless to say, "Printers" won't print a test page.

Hardware: Desktop PC with Asus A88 XM-A motherboard;

   hp LJ 2100M is a dual personality PostScript printer about
          17 years old. Connection to system unit via USB-PrinterPort
          adapter cable which has worked well for the past 10 years.

Software: Ubuntu 14.04.3 (AMD 64-bit desktop) newly installed
          (yesterday) over a previous unsuccesful installation from
   day before. (It all worked well until I tried to install
           Skype.)

   Printer driver (which worked in the past) is
             HP LaserJet 2100M Foomatic/jet4.

Things done:
     (a) Attempts to force a Device URI to USB: etc (see above)
   don't work.
     (b) Printer setup Firefox via about/config
     "print.postscript.papersize=A4"
            "print.print_color=false"
            "print.print_paper_size=0" (as I found it)
     (c) Printer setup ThunderBird via Edit; prefs; Advanced;
            Config Editor. as for (b) above
     (d) LibreOffice printer setup as root:
           Hand modify file psprint.conf
           gksudo gedit /etc/libreoffice/psprint.conf
           with edits:
               pslevel=2
               colordepth=8
               ColorDevice depth=-1 ( for grey-scale)
           deleting the initial semicolon on the line , which I assume
           indicates a comment. (Please correct me if I'm wrong)
         Check via sudo /etc/libreoffice/program/spadmin.

Thanks in advance for any useful help you can give.

Mike