Causes

The modem isn't being seen by the computer at all
The dialler is sending an invalid modem init string to the modem

To determine which of these is the case:

1. Go up to the menu, choose "Control Panels" and select "ConfigPPP". You should now see this:
   

2. Put an "X" where is says "Terminal Window"
3. Click on "Open" You will now see this:
   

4. Type "atz" and hit "return". One of three things will result:
   1. "atz" typed into the terminal window, and "OK" appeared after you hit return
   2. "atz" typed into the terminal window, but "Error" appeared after you hit return
   3. Nothing appeared in the window.

   The first two simply mean that in invalid init string is being sent to the modem. The list of Mac modem inits should give a good insight into what it should be. Nine times out of ten, all that is required is either "AT&F" or "AT&F1", depending on the modem. Try a few out in the terminal window until you get one that returns "OK." Once you have that, you can enter that string into the modem setup and things should be dandy.

   The third one (can you guess?) can mean one of a couple of things. Chances are that there is an extension conflicting with the PPP extension.

If this doesn't do the trick, we try for the left-field solutions.

• Is the modem new?
  • The modem cable may be bad
  • The modem cable may be loose
  • The modem port may be bad
  • The modem may be bad
  • Was there a thunderstorm recently? Was the computer plugged in during it? Did the modem stop working after it? Ah-ha......
• Check the port name by bringing up the FreePPP Setup and clicking on Modem Setup...
  • There is occassionally a setting under port name labeled "Internal Modem" to be used for *gasp* internal modems. If the setting isn't there, chances are it isn't needed, even if it is an internal modem.
  • If the modem is a PCMCIA card, there may be a setting for "PC Card." Try that.
  • If the modem is a GeoPort, there may be a setting for GeoPort.
  • Sometimes, just flipping the port name to an incorrect setting (like Printer Port), restarting, and flipping back to the correct one is all that's needed.
• If the modem has been used before, and none of the above has made any difference, it's probably time to a) Call 1-800-SOS-APPL and ask Apple Tech Support what's up and/or b) Have a diagnostic run on the modem, the cable, the port, or all three.