If you look at the FreeNAS console, is the IP address that's displayed, the same one you are using. Or, if you are in the console, type: ifconfig
Also, from the console, can you ping your router?
If you allow DHCP, can you switch it back to DHCP (item 1 on the console menu) and try the address it gives you.
Lastly, do you know what kind/version of NIC you have?