I'd check 2 things.

1. Make sure that your computer and the network port are set to the same speed and duplex (10/100 and half/full). On my own PC once when I swicthed ports the duplex on the swicth was set to full and my auto-sense on my own NIC for some reason went to half and I was unable to browse the Internet (basically lost TCP/IP). You may want to manually specify your NICC speed and duplex rather then rely on auto-sense.

2. Your ports may be VLAN ports in which case the port will only recognize a specific subnet of addresses. Check with your network admin to see if this is the case.