Make sure that both computers are on the same work group name ie: workgroup. Make sure if your using the routers DHCP server, to set your nic cards to obtain IP address automatically an dns. If you have inputed your own IP address, then make sure its like this: Router IP 192.168.254.1, then make comp1 192.168.254.2, comp2 192.168.254.3. If you crimped your own wires, make sure they are correct. See if any of this helps, these are the main causes of your problems.
Zypha