i was using my xp pro box tonite, just surfin the net and stuff like that when i got this popup box from the OS saying that nt authority\system has authorised a system shutdown, then about aminute later the computer shuts down for no reason at all, why would this happen?

i have some of the XP log files but im not really sure what it means

Event Type: Error
Event Source: Userenv
Event Category: None
Event ID: 1512
Date: 14/06/2003
Time: 7:55:23 PM
User: NT AUTHORITY\SYSTEM
Computer: PHROSTY-BOI-WIN
Description:
Windows cannot unload your registry file. The memory used by the registry has not been freed. This is often caused by services running as a user account, try configuring the services to run in either the LocalService or NetworkService account. If this problem persists, contact your administrator.

DETAIL - Insufficient system resources exist to complete the requested service.

i dont know what to make of it, before this happened i also got another error from some windows part:

Event Type: Error
Event Source: Winlogon
Event Category: None
Event ID: 1015
Date: 14/06/2003
Time: 7:54:22 PM
User: N/A
Computer: PHROSTY-BOI-WIN
Description:
A critical system process, C:\WINDOWS\system32\lsass.exe, failed with status code c0000006. The machine must now be restarted.

ive never had this happen to me before and have been considering a format of this machine for a while to start ona fresh new install, is this a good sign that i should be formatting soon?