Can you browse by IP address? For instance,
try http://www.mozilla.org then 126.96.36.199
Also, click on Start
and paste the following into the Run box, exactly as shown, including double quotes:
cmd /c "ipconfig /all > postme.txt & ping yahoo.com >> postme.txt & notepad postme.txt & del postme.txt"
and press ENTER
A file will open in Notepad. Please copy and paste the contents here. Close the Notepad window and the file will be deleted and the Command Prompt window will also close.
That will tell us a lot about your network setup and configuration.