BleepingComputer.com: Cannot Access Internet even though connected

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I upgraded my Vista Home Premium x64 to SP2 on 8/28. No problem until 8/31. Now I cannot get on the internet regardless of firefox, IE, or Chrome. The Windows Network Diagnostics did not find any problems. The network and Sharing center shows that I am connected to my network and then to the internet with no issues. IPv4 = Internet. IPv6 = limited.

Steps completed thus far:
> I rebooted the cable modem and the router (linksys wrt54g)
> I successfully pinged the x64 computer with a different cpu on the network. Status activity shows bytes sent and received successfully on the x64 system.
> I tried to system restore prior to SP2 upgrade but says failed, however System properties show that running SP1. (???)
> I updated network card driver (intel 82567lf-2) to most recent - 7/23
> I ran the Intel network card diagnostics and all test were sucessful
> Booted into safe mode with networking. Unsuccessful.
> Ran Hijackthis, nothing unusual.
> Plugged x64 network card directly into cable modem bypassing router. No dice.
> I am at a loss of what to do. I do even know how to describe the situation succinctly enough to search and see if others have had the same problem. My computer is a Dell XPS Studio Core i7 w/ x64 Home Premium. Please help.

Also I am now getting the pesky Data Execution Prevention message after ever window that I close. I tried to do the bcedit.exe fix, but said that bcedit wasn't recognized.

You might want to disable IPv6 networking support and see if you connect.
The HJT log you attached says you are running Vista SP1. Are you sure your update to SP2 worked fine?