It would seem that the user has an analog modem that worked for faxing until
he installed a broadband modem. Given that the user did not say if the
analog modem is still installed, this might be the problem. On the
otherhand, it's not uncommon to have the fax services get screwed up by
changing internet access from the analog to the broadband modem, even if the
analog mode is still installed.
The last time I had this happen was with win XP SP1a, and ended up
reinstalling an external serial port modem.
That allowed me to reinstall and configure the fax services.
Since windows XP fax service can be "flakey", even with a reference standard
modem such as a USR external modem, I normally use an external all in one
for fax service. The original problem with Fax and general modem operation
with XP chased back to how the microsoft module that parses modem reply
strings worked. It, for whatever reasons, can see random characters leading
the modem reply string. This fools the parser into thinking that the reply
string is something other than what it is looking for, and it does a bailout
to defaults. This allows normal analog modem service to work, with possibly
incorrect modem status and connection information passed back. A modem
service or application such as Fax, that requires specific modem replys,
will operate intermittently, or fail. At one time there were some
undocumented fixes that improved matters. I have no idea if there was any
further action or patches that would help. As I remember the undocumented
"patches" involved changing some registry data that in turn did something to
the data transfer process used to get the data to the parser.