IIS4 won’t serve pgs_svc not off_no logs

I have IIS 4 on an NT 4 SP6 box hosting our website. I’ve shut SNMP off. Ever so often the site gets hung during the night. Requests for pages time out remotely, and on our lan the files aren’t found. There is no log of bizzare activity and all I need to do is restart the WWW service and it’s fine. Any ideas?