Windows 2000 server shudown

hi all, i m in problem , we have windows 2k server
that gives an error that “the system is going to shutdwon within 60 seconds, save your work and logo off, initiated by windows nt authority ,and
the process is by c:\windows\system32\lsass.exe”
i think my server is infected by some worm or virus. we are getting this error in all xp prof. system too.
plz help