My sudden loss of network connectivity was caused by a disabled Norton Internet Security application on my machine. Despite having disabled it after my subscription ran out in August of last year, I manually ran the Symantec "Smart Updater" and my capabilities came back. Grrr... I dedicated 4 3/4 hours to debugging this problem, not to mention the inconvenience it's caused. I HATE SYMANTEC!!!!!!
So, to aide Google searches (human readers, feel free to ignore):
Symptoms: I first noticed that my IE couldn't connect to secure Websites on the road,when I was connecting via WAP. When I got home, I noticed that also redirects weren't working. I installed Mozilla and Opera and was alarmed to find that they can't reach any Websites at all. I wrote a simple HttpGet program and found that my own code couldn't reach outside Websites, failing with a SocketException.
Within my own subnet, though, Mozilla and Opera can access my Websites on other machines, so the problem is not within the IP stack (which I reset, anyway, MS Article Q299357. I also deleted my network card and let it reinstall.).
Other machines on the network can access secure Websites, so the problem is not in my WAP.
I installed netmon.exe on Windows XP following the recommendation at this Web Site (I actually snagged it from my Windows Server 2003 install). I determined that packets weren't leaving my machine at all.
I reset the TCP/IP stack by running "netsh int ip reset c:\ip_reset.log" I deleted my current Winsock registry keys following this advice. I tried running the winsocks repair facility at that same site.