Well, the obvious action is to make sure that all your wiring looks good. Make sure you have your splitters configured properly for cable modem service, and that everything looks like it's in good shape. Read the other modem sections to get your signal levels and troubleshoot from there.
If you call technical support, they generally keep a log of your cable modem status, such as downstream power (signal it's receiving), upstream power (how hard it's working), and upstream and downstream snr (signal to noise ratio).
They can look at this chart and tell you if your modem has always had bad signal or if it's something recent.
If they tell you that the line has too much noise on it, this usually means that the shielding has been damaged on a cable somewhere, or you have a really nasty connection somewhere.
If your modem drops in and out even though all your signal levels are good, then it's most likely a loose connection somewhere or a plant (outside of your house) problem.
Please note that if your cable light never goes out but you lose connectivity, it's most likely something down at the cable company, but CAN be a bad modem, or something wrong with your computer. This is not an RF (signal) issue.
If the cable light DOES go out, then it's an RF issue and you need to start looking at the other troubleshooting sections.
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