I have a problem that has been plaguing me for the longest time.

We have windows 2000 server, SP4. On it is loaded SQL Server 7, SP4 and a
couple other small apps, nothing major. We use it for SQL and file sharing.

Every 5-7 days the thing locks up with Lsass.exe at 100%. We we eventually
get server errors about memory and it reboots itself. During this time SQL
server locks up and everything stops responding.

I have tried spyware removal tools, periodic reboots of SQL server and virus
scanning. Nothing turns up.

I'm not sure what to do. I have been thinking of rebooting the server every
2 days, but am dumbfounded by the situation. Any ideas on what it could be?
Should I re service pack the machine?

Thanks,
Ben