Not all that sure regarding the newer versions of free zone alarm--but some of the older free zone alarms had problems with networking---but I have heard that the new versions of the free zone alarms are bloatware that will bog down anything but very fast modern PC's.
As it is, I still run the free sygate 5.5 firewall---which is small, effective, and very network friendly. In contrast---many use AVG with no reported networking problems. I use Avast AV---and I have heard of very few reports of any AV programs causing networking problems. But there are a number of free firewalls---so you might experiment in finding some that network better---if nothing else---you may choose to go back to zone alarm.---try a security site like spyware warriors forums for various other firewalls to try.---or castle cops.
But many firewalls can be shut down after boot---if you can't see the network with the firewall on---and see the network with the firewall shut down---you know the problem is with the firewall or its networking configuration.---but don't do the experiment while connected to the internet---I just get this creepy crawlie sensation when my firewall is shut down.---I'll endure it for the purpose of a quick experiment---and then re-enable my firewalls as quickly as possible.