All computers show up on Network Map but can't access them

I have two HP Pavilion desktops runing Windows 7 and one HP Pavilion notebook using XP. I have set up HomeGroup on both desktops and downloaded the LLTD responder on the notebook. Both desktops have network discovery turned on and file and printer sharing turned on. The first desktop network map sees all three computers and can access all files of the laptop. It can access the public files and the external hard drives connected to the other desktop, but I get an error trying to access the C drive (need permission to access). The laptop cannot see the second desktop. I get a not accessible error message when I try to access the C drive of the first desktop. The second desktop network map shows all three computers, but nothing happens when clicking on either the first desktop or notebook icon. For now, I have uninstalled Norton Security Suite from the second desktop and the notebook. The first desktop has Norton Firewall turned on. Any clue as to why the second desktop will not access the other computers?

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