With no OS mentioned, I can't tell you any direct actions, but for XP, firewalls are the number 1 reason I see people fail at making a network. Next are things like.
1. Didn't install drivers.
2. Invalid configurations (example? Cable modem to hub, PCs to hub, no router)
3. Didn't ask the USER account to the XP machine and the client...
http://www.wown.com has most of this. I don't duplicate that content here.
I finally have a network. When I clik on "View Workgroup Computers" I see the computer I am networked to.
When I clik on the computer though, I get an error message:
This computer is not accessible. Please contact the server administrator to see if you have permission to access this computer.
I set absolutely ZERO security.
Could it be those pesky firewalls?