For starters, if resetting the cable modem resolves the issue temporarily, that would be a good place to start. Also, I have known it to happen that if you run file sharing programs on lower end routers, you basically end up causing them to run out of memory from all the activity, and then this sort of thing can happen.
So if you have any kind of file sharing program running you should probably stop, or at least learn to reign it in to avoid these issues. Otherwise, I would probably start by getting another cable modem and/or calling the cable company and getting them to verify there's no issue with the physical connection between the neighborhood hub and your place.
My internet is going out a couple times a day. I have to unplug the cable modem to bring it back up. Where should I start? What should I look for?
I've been having problems for a few months now but just recently has it got worse.