Nis 2009 is blocking my local network

Hi,

 

I have NIS 2009 and 2 PC in my local area network. Strange things happens and no way until now to manage start browsing Web on the PC's simultaneously. If, I activate local area my first PC (server) is stoping to browse any web pages (so hapens to the second one). If I deactivate the lan, all is good. If I deactivate the Firewall from NIS (with lan active), again all are OK, both are running. No way to resolve something with NIS Home Network settings (including all sort of settings targeting the trust levels, IP's of both PC's, etc). Please, have a valid solution for this problem, cause I won't pass to another antivirus after long years of fidelity to Norton.......?