this is extremly odd. I have been running a squid proxy server for about a month now, i am also running a webserver , i have a windows and a linux computer behind the proxy. I have been browsing the internet fine the whole time after i initially got the proxy setup.
Yesterday i did nothing to any of my computers, all i did was restart my webserver (apache) but that would do anything to my internet. My linux computer just would go onto the internet. i restarted my computer (that always seemed to work for windows) looked through all the browser settings of both Mozilla and Konqueror 3, it still wont work. In konqueror it says cant connect to proxy 192.168.0.1 at port 3128, but my other computer with windows connects fine. I tried using webmin "http://127.0.0.1:10000" and for some oddd reason the same message came up... this isnt right, its the loopback interface its not supposed to try to connect 192.168.0.1:3128. I can ping my internal interface on my server fine (which means it isnt just a loose cable), i cant ping the external interface on my server. I checked over the proxy settings again, i cant remember changing a thing, but the internet still wont work on my linux machine. i can also do an "nslookup" and "whois" from my linux machine.

what happens if you do a ifconfig eth0 down then up ?? what output does ifconfig give you and or route for your default route ??