Are all the lights on? Usually when you don't have an internet connection, the internet light won't turn on - or stays red.
Here is a quick way to test if you have internet on a PC:
Open: Run, type CMD. Then type "ipconfig" without the quotes and hit enter. If it says "hardware disconnected", your computer is broken. (call tech support)
If it gives you a bunch of numbers, type: "ping -t www.google.com" and hit enter, if it says "pinging google with XXbits..." then you are connected and there is something wrong with the browser/or a non hardware related issue.
If none of this works, call the ISP - if its comcast, remember to install the comcast CD first, on all new computers entering the network!
lulz