check the static IP of the modem if it is constantly 0.0.0.0 it has been de-registered and needs to be reacticated at the ISP end which means phoning up.

does the cable light illuminate on the modem i.e. the data cable light.

I have three lights on my modem (telewest) POWER, PC, DATA, CABLE.

The cable light is always on. This verifies the modem is ready for transmission through the cable.