cannot conect to Ubuntu servers

[XEtedBear]

I've been having internet connect problems. After fiddling about I now have access to any new URL I care to specify (i.e. I'm not being fooled by a cached set of web-pages), but I cannot use the Ubuntu Software Centre (Failed: check your internet connection), nor can I search for the best Ubuntu server. But I can access www.ubuntu.com

I'm confused by this. Can somebody advise a next step?

[mcduck]

Are you behind a proxy of some kind? In that case you'll need to configure the proxy settings system-wide, not just in your web browser. You can do that in System Settings->Network->Network proxy.

[XEtedBear]

I have no idea what a proxy is, so I guess I don't have one - and I certainly wouldn't know how to configure one if I did.

What do I do in the case where I don't have a proxy ?