Restart Problem with 2000

Restart Problem with Server 2003
We have Dell Server having Windows Server 2003, Enterprise Edition, installed on it. But from last few days , a problem of restart have been created on it.
After booting, a message appears on it any time, and counting begins that in 60 sec your system would be restarted.

we have installed all patches, updates on it as desired by it.

This is “lsass.exe” file problem.
Pls help.