Hey there
Make sure that IE and Firefox's Proxy server boxes are empty and not checked. Chances are 80% that it is the problem.
Try uninstalling Firefox and reinstalling it (When istalling it, select the option of "NOT importing settings from other browsers")
If you open command prompt and enter "Ping www.google.com" and if gives you a responce simular to "Pinging
Google [209.85.229.103] with 32 bytes of data:" then your browsers should work and settings have to be checked.
Hope this helps...