I know you've got around this, but I thought I'd add my 2 cents worth for someone elses future reference.
In this kind of situation i always find it useful to jump into the command prompt and use ping and tracert. They usually give pretty good errors (assuming that the hardware is present and working).
If you try and ping a domain name that you know exists (for example 'ping www.tfproject.org'), you'll quickly see if you have DNS working correctly. If this fails, you can find the IP address of the same 'known' server from another machine that works and ping that (e.g. 'ping 209.50.251.11' - this is the IP address of
www.tfproject.org atm). If this also fails, then you may have an issue with your connection to the gateway. This is where tracert comes in handy - doing a 'tracert 209.50.251.11' will conclusively prove whether you have a working gateway...
This at least gives you the basic answers about your connectivity.