Yesterday, just before I went out to the store, I began the installation of the latest security update for WinXP. When I got back, all my Internet service was blocked.
Not thinking through completely, I went through the 'modem reset/computer reboot' routine three times before calling TimeWarner to see if there was a network problem. There wasn't. They tested their side, pinged my comp... no problems. But still no service. The local office handed my call up the chain to the RoadRunner network tech support folks.
As soon as the rep asked what firewall I was using, she said "We've been getting a lot of calls from ZoneAlarm users - try turning it off and see if you connect to the Web." I did, and I did.
Turns out, it was the XP update conflicting with ZA -- which I learned after the fact, here:
http://download.zonealarm.com/bin/free/pressReleases/2008/LossOfInternetAccessIssue.html
Installed that patch, and everything's as usual again.