Yes, I have "successfully accessed network from xp mode virtual PC"
You may have accidentaly disabled or not setup something properly.
What is the IP that you are getting. if it is a 169.x.x.x then that is Automatic Private IP Addressing (APIPA)
This happens when DHCP is enabled and the network can not pull an IP from the DHCP server.
This (for me) is not easy to fix through a forum like this.
All I can say is to maybe uninstall/reinstall Virtual PC with XP Mode as it should be setup automatically without you having to do anything.
Or check that an app you installed didn't make some change to network settings in XP.
Or, if you have Internet Security Suite (of any kind, they are all crap) uninstall it (or turn it off) and see if maybe...