This might be a silly question but,
Have you turned your modem off by the mains (Totally disconnect it from the power supply.
I used to turn my Amiga off by the power button on the tower, turn off the monitor & just forget about the modem.
As it turns out, the modem needs to be reset sometimes & you can do this by pulling the plug for about 5-10 minutes (To be safe), then, when I plugged it back in again & rebooted my Amiga, it was fine.
Hope this is some help.
