Q: My Internet connection, which I get through my cable company, has been intermittently dying on me, but my television works fine. When I unplug and replug my modem, the service returns a few minutes later. How can I diagnose where the problem is?
A: It’s fair to conclude that you don’t have an overall connectivity problem, since your cable Internet runs over the same coaxial (and sometimes fiberoptic) network that your TV signals use. In fact, in most cable networks, Internet transmissions are sent over a single 6-MHz band–the same amount of spectrum allocated to an individual cable TV channel, and just one of the hundreds of similar-capacity bands on the wire.
There are several possible causes of your Internet outages. First, you’ll want to rule out the possibility of a bad connection on your home network by plugging your computer directly into the Ethernet port on your cable modem. Then try rebooting both your computer and the cable modem (unplug it, wait 10 seconds, then plug it back in). If your Internet connection returns anytime during this process, it’s possible the problem is with one of the components of your home network (router, wireless access point, etc.).
Then again, maybe not. Cutting the power to the cable modem causes it to reboot as well as resync with your cable provider’s “local office.” This can solve the immediate connectivity problem–it’s what you’ve already been doing–only the trouble will rear its head again later.
If your cable modem doesn’t attach to your computer with Ethernet, but instead employs a USB cable, make sure to check that Windows’ Device Manager isn’t turning off USB devices to save power. (Go to the Control Panel, select Device Manager, then check USB Controllers.)
If the problem isn’t with your home network or your PC settings, you may be “losing your lease,” which means that for some reason your PC has lost the IP address provisioned by the cable company. Check your IP address (launch Run and type “cmd” then “ipconfig/all”). If it starts with 192 or 10, you may have lost your lease.
Unfortunately, periodic disconnections can be strange voodoo. I lose the connection on my home cable modem every week or so. Technicians from the cable company have come out multiple times, run new cable and done all the proper tests, yet no one can figure it out.
One final tip: If the “cable” light on your modem is off or flashing, it’s almost certainly a problem with the wiring between the cable company and your home.