It could be that the adapter is not configured correctly.
Or could be a conflict.
To configure your LAN adapter:
Open Network connection, right click on your LAN network icon, click properties.
Then click in the list: Internet Protocol (TCP/IP) so it is highlighted. Do NOT remove the tick.
Then click properties.
In properties you need to select the blob next to use the following IP address:
Insert: 192.168.0.1 for the main PC. and for the second PC connected: 192.168.0.2
Then both PC's have the same subnet mask of: 255.255.255.0, windows may add this for you anyway.
Then in use the following DNS server addreses: Add the computer IP with Internet connection sharing if you have it this is normally the main PC: 192.168.0.1, otherwise leave blank of you do not use it.
Then click Ok.
Reboot, see what happens.
If not try looking for error messages or conflicts in eventvwr.msc from the Run command.
Post them here and someone will help.
Hope I have been of help.