Browsers can't establish a connection

I keep getting errors in when I try to surf the net: Firefox can't establish a connection to the server at ...

I think maybe there is something wrong with a terminal command, but I don't know enough about it to clear it!

I have Lion and I have never had this problem before. Compared my network settings to my mac book and they are the same.

I can connect via mac book and ipad. One site suggested I reinstall Lion. But, I got it from the App store - wish my "server can not connect to"

If reinstalling lion is the fix, I guess I'll pay for a box copy. Just want to be able to surf again. No parental controls are set. HELP!