I had a very strange networking issue last weekend. After connecting to corpnet via VPN and direct hookup, I was able to ping all remote servers, but was not able to do anything, such as web browsing and remote desktop. It was not the first time that I faced this issue, and helpdesk told me that IPSec settings may have messed up.
The following set of commands has helped me flush settings related to networking and IPSec, and restored my corpnet connection in both situations.
1. Launch a DOS command prompt
2. netsh int ip reset all
3. netsh winsock reset
4. ipconfig /flushdns
5. nbtstat -RR
6. gpupdate /force
Akin to "Ctrl-Atl-Del" of your networking settings, this series of commands should flush IP interface, DNS, Winsock, NetBIOS and group policy settings.
Good luck to troubleshooting your networking and IPSec issues.