Mullivar - the port is "USB: Virtual printer port for USB" with the correct printer details shown. The check box for bidirectional support was also found checked and left at that.
Whilst in the printer properties window I went to the general tab and (for the hell of it) clicked to print a test page - and it did, together with all of the usual Lexmark status and ink level screens coming up as well.
Somewhat stunned, I opened a MS Word document and hit print - it all went fine again.
I'm stumped (but very happy) as the only thing done since the last re-install and reboot when it failed, was to have turned the PC off that night, then on again this morning.
I still don't feel that I fixed anything here, but it's working so I am happy and will not puzzle over it too long.
Thanks for the assistance people - much appreciated of your time; great forum as well.