Modem won't hang up any more!

alt.comp.hardware, alt.comp.periphs

As of two weeks ago, I can no longer Internet-connect
the usual way, via my Supra Express 56k modem. (My OS
is Windoze98.) Here's the problem:

I need to unplug and replug the telephone line going to
the modem, to restore the dial tone. If not, the phone
line remains open, so I can't receive or send phone
calls. It's as if the modem lost its ability to hang
up. (Problem remains even when my computer is shut
down...so I know it's not OS--or even
computer--related.)

Now, when I don't need to get on the 'net, I unplug the
phone line from the modem, and plug it into the back of
my answering machine... which then allows me to receive
and make regular phone calls.

Is this a burnt-out modem chip? Or can I possibly
restore my modem to its former excellent condition?
Where do I start? I have yet to find the appropriate
help file. If you know of one, please direct me to it.
Otherwise, I'd much appreciate someone guiding me
through possible maneuvers to correct the error.

TIA.