A week or two ago, I lost internet access. I checked the router and the settings were not changed. The other computer had internet access. I checked my ethernet cable, my ethernet card, and fiddled around with the Windows network settings with equally negative results.
Turned out my problem was following the Windows Automatic Updates’ recommendation to update to XP SP3. A whole bunch of people had the same problem as me after installing SP3. They would receive the “limited or no connectivity” message on their network icon and pull their hair out trying to find the cause.
A simple uninstall of SP3 through the Add or Remove Programs tool under the Control Panel fixed the connectivity issue.
Forward three weeks later, the automatic update from Windows struck again, installing a security fix which seemed to fix my internet connection to not allow me to connect. Again, the only workaround was to uninstall the fix. And turn off the automatic update so this does not occur again.
This may have been a ploy by Windows to push everyone towards Vista!