Critical Porblem

Hi All:
i am facing a critical problem on my server, i have windows 2000 server with service pack 4, mailer Daemon, and ISA server 2000 all machines are on workgroup. The problem is that after 15 or 30 minutes this server out from network. when i search other systems error appear” A specified authentication packages is unknown”, and in event viewer Lsasrv show this error “the security packages negotiate generated an exception. the package is now disabled. this exception information is the data.”. But after restart computer(server) everything is O.K for 15 or 30 minutes and this web site automatically run ” http:\\ereetz0rz.100.com/index.html”.

pleaze help me

thank you