I have a MBP 5.1 OS X Ver 10.5.8 2.93 Inted core 2 duo

The Ethernet intereface shows connected, but I cant ping across the network. I can ping the local interface, when I have a static IP configured, but not across the network.
I tried a x-over cable to a known good PC, both Static addressed. The ethernet showed connected but still could not ping the other PC.
Tried DHCP, no luck when connected to a known good ethernet switch port.

Wierd thing. When I rebooted the MBP, just before the login screen. The PC which was set for constant ping, I got 4 responses. I duplicated this. Once the MBP finished booting, no network connectivity.

Tried all different combinations in Network Preferences.