Sometimes, when powering up a Power Macintosh G3 All-in-one (AIO) with an Apple Desktop Bus (ADB) modem attached, the modem doesn't always initialize correctly. It may immediately go off hook, or not respond to AT commands, for example.

Customers have reported this behavior with some, but not all, modems that receive power from the Apple Desktop Bus. Modems with a dedicated power supply that plugs into a wall outlet do not show this issue. If restarting or shutting down and starting up the computer does not seem to make a difference, then either resetting your modem (assuming it has a reset button) or disconnecting and reconnecting the modem's ADB cable should resolve the issue.