printing .pdf's

I have used Acrobat for many years, but all of a sudden I find I am unable to print .pdf files from various sources.  When the print screen comes up it seems to default to sending a fax (it is an HP multipurpose print/copy/scan/fax machine) and whatever printer I select from the dropdown box it ignores and reverts to the fax output.

I have checked the default printer settings on the system;  I have uninstalled and re-installed Acrobat DC (the free version): but all to no avail.

Until a few weeks ago it was working perfectly.  What has changed and how can I fix it?