no internet when manually assigning IPs

If i assign my Mac Mini its own ip, say 192.168.0.50 as i want it to access the same IP each time, it doesnt connec to the net through my DG834PN router. If i move the IP assinging back to automatic, it gets assigned an IP and connects to the net.

Any ideas why this item wont connect to the net through this router when UIP is manually assigned? Mini is wired to the router