Most likely a signal issue. See modem troubleshooting section.
Feedback received on this FAQ entry:
This is 100% true. I've also noticed significant improvement in my digital box performance after switching to a battery backup. I'd certainly recommend connecting networking equipment such as routers to a battery backup too.
2012-11-30 00:21:31 (S1R1US)
A large majority of problems reported with cable and DSL modems that are repaired by resetting or rebooting are caused by flaky power. An uninterruptible power supply (UPS) is a MUST for any computerized equipment if you expect reliable service.
If you already have your equipment protected by a UPS, check and replace the batteries every 2 years. This is well worth the savings in irritation from failures of equipment on which we depend more and more.