Finally discovered that the cable modem was flaking out. Seemed to be getting power, but not steadily or sufficiently. I happened to have a spare power brick that puts out nearly the same amperage, and at the right voltage and polarity, so I plugged it in and YAY! Cable modem's not dead, just the cheapass power brick that came with it!
Running on reserve fuel cells for now, need to hit radio shack and get a replacement tomorrow.
close freakin call.