Check your network settings to make sure that .org didn't get added to your domain search order as some kind of "always use" - or try going to the google site through its IP address - type
http://216.239.51.99 in your browser (at least that's what my nameserver says its IP is) and see if that works. If so, then it is most likely a DNS problem.
Sapper might be right that your ISP or their provider is having DNS issues so maybe you should talk to them if that is the case.