WAN adapter stop respond

Hi!

I'm using a Windows 2003 Server R2 with two ethernet adapters. The first
adapter in configured to WAN with my valid IP's, and the second adapter is
configured to my LAN with my private IP's.

The WAN adapter is stop responding to requisitions from internet. When I try
access my server from a external network, with a PING, for example, the
adapter don't answer. If I make same PING from my internal network, the
server reponds ok.

However, after REPAIR then WAN connection, it come back to function very
well for some variable time.
I'm using Windows Firewall and it's logging some attempts of scan in many
ports such TCP445, TCP139 and others. There any Windows action protection
that make my WAN adapter stop to responding to internet connections?

Thanks for any help,
Andrew