Limited or No Connectivity Error
Today, I spent a few hours helping to clean up a friend's computer that hasn't been serviced in over 2 years. The first thing I did was uninstall the user's non-functioning antivirus program (the definitions had expired several months prior), booted into safe mode and removed a handful of virii using Symantec's Automated Support Assistant. I then installed Norton Antivirus and did a complete scan of the system.
Next step was to check and remove all unwanted startup programs in the registry, in the Startup folder and running services. Silent Runners does a great job of identifying and reporting all Windows startup programs (it's a small effective VB program that uses the WMI). I then installed two spyware removal tools, AdAware and Spybot Search and Destroy. I finished up by cleaning up the Temp and Temporary Internet Files folders and defragging the system using VoptXP (a very fast defrag utility - much faster than dfrg.msc).
After I was done, the internet connection stopped working and I started receiving a "Limited or No Connectivity" error. I tried a variety of strategies including re-installing the network card, checking the physical connections, ect. The culprit was corruption in Winsock and the TCP/IP stack (undoubtedly caused by the spyware). I used the Winsock XP Fix tool to do the repairs (it's actually a VB implementation of the information provided in Microsoft KB article 299357 - How to reset Internet Protocol (TCP/IP) in Windows XP).
Here is a link to the repair program:
http://www.spychecker.com/program/winsockxpfix.html