Windows 7: Homegroup not working correctly

This is a wired connection issue.
My ISP is Northland Cable of New Caney, TX
My broadband connection type is cable.
My Modem/Router Combo is ARRIS TG862.
My firewall is Windows Firewall, antivirus is iolo System Mechanic Pro Version 11.
My Homegroup comprises three computers, named CPU4, CPU7, and CPU8. All are running Windows 7 Home Premium SP1. CPU4 is 32-bit, the others are 64-bit. All computers have the latest Windows updates installed.
Output of CPU7 ipconfig/all is attached herewith.
The problem is that, while CPU4 and CPU8 can both see the other computers, CPU7 can only see CPU4.

Homegroups doesn't have much to do with machines seeing each other. That is more of a network discovery function.

The fact that certain machines can only see some machines tends to point to the anti virus as the culprit.

I would need to see the ipconfig/all from each machine to make sure they are all in the same subnet.

I have attached output of ipconfig/all from CPU4 and CPU8

The ipconfig's all look good. I'd suspect that somehow the anti virus is blocking those machines from seeing each other.

I have uninstalled iolo System Mechanic Pro from both CPU7 and CPU8.
This did NOT fix my Homegroup problem.

Are the other machines showing up under Network and under Homegroup?

Each computer can see itself and the other two in the Network folder.
CPU4 and CPU8 can freely access shared files on the other computers.
CPU7 can freely access shared files on CPU4.
When CPU7 tries to access CPU8, it is prompted for a Network Password.
As far as I know, there is no Network Password, or if there is, I do not know what it is or where to discover it.