Sharepoint stops working

I am running a Small Business Server 2003 and noticed recently that Sharepoint just stops working. If I try to connect to it on our intranet I get error 10054, connection reset by server. I checked IIS and it reports it as running. If I try to get to the admin from IIS I also get an error stating this page can not be displayed. I have tried restarting IIS, no success, restarted the ISA firewall, no success. Complete restart of the server and Sharepoint works again.
Not sure what else I should be checking. Even installed SP2 for Sharepoint and nothing.
Any ideas what to check next?
Thanks in advance