I replaced the modem in a friend's computer because it started getting a "No Dial Tone" error with a new US Robotics modem. Some time after that the US Robotics modem failed with the same "No Dial Tone" problem. I had it replaced under the warranty. Now the replacement US Robotics modem has the same "No Dial Tone" problem. Why is this happening to all of his modems? These are all internal PCI modems.