Open a command prompt (start-run-cmd) and <font class="small">Code:</font><hr /><pre>ping google.com</pre><hr /> and see if it resolves google.com an IP address and if it replies. Try a couple of other sites too, they should all resolve to an IP address and get replies.
It should look something like this...
<font class="small">Code:</font><hr /><pre>Pinging google.com [72.14.207.99] with 32 bytes of data:
Reply from 72.14.207.99: bytes=32 time=89ms TTL=234
Reply from 72.14.207.99: bytes=32 time=86ms TTL=235
Reply from 72.14.207.99: bytes=32 time=92ms TTL=234
Reply from 72.14.207.99: bytes=32 time=87ms TTL=235
Ping statistics for 72.14.207.99:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 86ms, Maximum = 92ms, Average = 88ms</pre><hr />
I am betting that you will get the names resolved to IPs and get replies.
If your PC is set to use DHCP, the at the command prompt issue <font class="small">Code:</font><hr /><pre>ipconfig /renew</pre><hr />
If you get an error that goes something like "operation can not be preformed on something not a socket" you have spyware or another application that has screwed up your TCP/IP stack and you will need to get some spyware removal tools and repairs tools to restore proper function.