JNickel101 said:
Open IE
Tools - Options - "Connections" Tab....LAN Settings Button....
Do you use a proxy server?
Or...
open command prompt
ping
www.cnn.com
write down the IP address that resolves for cnn.com
Open IE
in the address section, instead of typing
www.cnn.com , type in the IP address...see if the page comes up.
Do like Jnickle says and try running a ghost.
I had the same thing going on and eventually resolved it, but it was one of those fixes, that to tell you the truth, I don't know exactly what the fix was.
Try running a new LAN setup in XP. This should adjust your firewalls and open up applicable ports.
What I think is happening is your pinging, but the reverse (ping) is getting the wrong IP (or maybe even the wrong address for your network card, port forwarding), some providers use transparent IP and use the address of the network card.
It is likely a port configuration thing, at some time your port configuration was manually setup and then somehow was changed. The default XP LAN port may work out for you, if not you may to have to manually configure.
To backup a bit, I'd check my passwords first and administrator rights, I know simple, but sometimes simple is the answer. Sometimes manual configuration requires additional passwords, not sure about XP.
A manual port configuration for XP tutorial may be helpful.
Modzilla has a force new IP tool that is also nice to have.