We had a windows 2003 Server that after a reboot we could not login to the Domain or get to the internet. Basically the NIC seemed to be non-operational. We could not Ping the server but we could ping the local loop and local IP. So I started troubleshooting routing and that led nowhere quick.
After looking at some issues with IPSec Service not starting I found the following MS KB. http://support.microsoft.com/kb/912023
I ran through the steps and noticed that the entire IPSec Registry Key was missing so I knew we were on the right track. Before running the command to recreate the Key and values I manually created the IPSec Key and Policy sub-key. Then ran the following command:
regsvr32 polstore.dll
And that did the trick! Server rebooted and came up normal with no issues.