do you use static IP addresses for your computers or not. If you do your two computers might have the same IP address or they might be on a different subnet.
If you use dynamic IP addresses, try giving each computer it own static ip address,
something like 192.168.0.1 and 192.168.0.2 with the subnet 255.255.255.0. And then try pinging one of the IP addresses. Oh ya that reminds me. The first thing you absolutely need to do is go into the run prompt in the start menu, on both computers, and type "ping localhost" (no qoutes), with everything plugged in and on. If it does not say reply from 127.0.0.1 and says something like Request Timed Out, then there is a problem with the NIC on the computer you pinged from. That can range from bad driver to the network being disabled in my network connections in the control panel.