I noticed this problem some days or weeks after upgrading my DSL line from 1.5 mbps to 3.0 mbps.

I've reinstalled the printer's software, but that didn't help. I've scoured HP's Support web site, but found nothing that I'd not already tried. I've checked the Fax Function settings and they seem normal. I don't mind buying another machine, but that won't fix the problem, if the machine itself is OK.
Any help with this will be appreciated.