I was having a number of strange network issues on a laptop today. Here's the complete nuclear option for resetting your whole IP stack. This is for when "Diagnose and Repair" isn't cutting it. Thanks to JohnP for his help.
UPDATE: On Windows 7, you'll need to do this to reset your network adapters:
Now, reboot and pray. Possibly not in that order.
Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. I am a failed stand-up comic, a cornrower, and a book author.
Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.