You can also try this as it sometimes fixes quirks that have occurred in network connections:
1. Under Device Manager (Right-Click My Computer, Properties, Hardware tab, Device Manager), find your network adapter under "Network Adapters", right-click on it, and select uninstall.
2. Next, right-click on anthing listed in device manager, and select "Scan for new hardware" or "Scan for hardware changes" - I forget the exact name.
3. Open Internet Explorer, and if it doesn't pull up a web page, close it down, and reopen again.
If you get nothing above, try the PING method mentioned by goombawaho above as well.
Basically reinstalling the network adapter driver forces the system to refresh all the network-related settings... well, don't know if it handles ALL of them.