watch out if you are running "nekkid" ... you need some sort of anti virus ....
http://www.free-av.com/
avira free is much better than AVG
do what vhg said!
(do that first)
if still no joy - I assume you're not using a proxy?
or hide my ip type progs
open a command prompt
type
ipconfig /all [press enter]
this should list your DNS server - it will show as your router) - (assuming you use one)
try your browser if no joy
at the prompt enter
ipconfig /flushdns [enter]
ipconfig /registerdns [enter]
ipconfig /release [enter]
ipconfig /renew [enter]
that will clear your entire networking cache
try again
oh and ignore jon