Mac Mini keeps losing network connection

Hey,

I have a Mac Mini 1.1 running 10.6.8, which I use as a headless media server at home. It connects to my BT Infinity 3 router via ethernet cable, and the Wifi is disabled. I connect to it remotely via dns through dyn.com. Other products sharing the network include 2 iPhones, an MBP and a windows laptop.

The problem;

Every few days, the Mac Mini will dissapear from the network and cannot be reached either through the shared devices menu or through Remote Desktop. Only a hard reset of the Mac brings it back. Can anyone help me identify what's causing this problem?

Thanks,

Tim