Just 1 PC connected directly to the modem? Or multiple PC's connected to a router then the modem?
If the 1 PC, Turn off PC and unplug modem for 1 minute. Power modem first so it gets connected (about aminute to be safe) power up PC..... If arouter envolved, all off, modem first wait a minute, then router, wait a muinute, then PC's....
Is there a splitter on the cable line from the wall to the modem? As in the one outlet provides signal to the modem and TV?