What you're calling a "WAN port" I would assume is your externally-facing NIC, that is, the one on which you hope to connect to the Internet. (To answer the first reply's question, though a bit of googling would've done the trick ...)
My question: have you tried another NIC? Perhaps the one you're using is not properly supported. You can use an old 10base-T one (but stick with PCI unless you want to fiddle around) if you like because even the fastest Internet connection short of a T3 will fall greatly short of 10 Mbps Ethernet speed.
A few more hardware details always help in these sorts of situations, so what's in the box?