Connecting to the internet: Mac finds ethernet, Network Connections Diagnostic says it's connected, yet no internet connection through Safari, Software Update etc

Hi,

I'm renovating an old mac for a friend, and I'm having problems connecting to the internet properly.

It is a Power Mac 3.6, and it's running Mac OS X 10.4.7.

I currently have an ethernet lead connected into the back of it, and I believe it has no wireless adapter. The Network Diagnostics Tool picks the ethernet up and says it should be working fine, also the mac has automatically acquired the day/time and can also show nearby devices (not sure how that is possible without some sort of wireless capability). Yet when I run Software Update, it says "A networking error has occured: timed out (-1001)". Similar problems arise when trying to browse on Safari or Opera, claiming "the server stopped responding" whenever I try an address. It seems to be that anything that wants to connect to the internet, other than Network Diagnostics and the clock, can't.

The ethernet lead seems to be fine, and does work (tested on a different device). The internet is functioning as normal and no devices connected to the router are having any connectivity issues.

Any help sorting this would be great,

Thanks!