Do you use ZoneAlarm firewall? Did you update Windows through Windows Update right before this problem started? Did this problem start in the last several days?
If the above answers are "Yes." you can thank MS for killing your internet access. The Update KB951748 conflicts with ZoneAlarm and ZA reacts by blocking all internet access.
The solution is to: a) Uninstall KB951748, b) shutdown ZoneAlarm, c) temporarily set ZoneAlarm 'security level' to medium, re-start ZA. You should now have internet access. Update ZA then re-install KB951748.
To uninstall KB951748: Start>Control Panel>Add/Remove Programs>ensure that the check box at the top of page (Show Updates) is checked>Scroll through the list to KB951748>Uninstall>re-boot.
Let us know if this fixes your problem.