We need more information.
This sounds like a modem connect issue. Which light is flashing? There are several on the modem. Each indicates a feature or diagnostic note.
Did you try consulting the users manual or your service provider?
What Linux product are you using and what version?
From the users manual;
Possible Solutions
! Check that the power cord is properly plugged into the wall outlet and the rear panel
of the SB4200.
! Check that the electrical outlet is working.
! If the Standby LED is on, the cable modem is in Standby mode. Press the Standby
button to reconnect Internet service.
! Press the Reset button.
! Call your service provider.