Network connectivity problem

I am running XP Home on a peer to peer network. After downloading an XP update, I can no longer access the internet or other computers on the network. I can ping all local ip addresses EXCEPT my own. My router is functioning as dhcp server. I can release and renew. All other computers on network are OK. I tried using XP recovery to prior date. Also, reloaded Windows in attempt to repair. Also installed new net card. Still no luck. Any assistance will be appreciated.