Windows server 2000 shotdown unexpectly

I have a Windos 2000 server standard edition, suddenly it has been shutdown unexpectly in random times, when I look in to the event viewer i found this message:

The process winlogon.exe has initiated the power off of computer on behalf of user \Administrator for the following reason: No title for this reason could be found Reason Code: 0x0 shutdown Type: power off

I have scan the server with mcafee
run the lsasser emoval tool
run the malware detection tool
uninstall and reinstall the sp2

but nothing resolve the problem

can you help me please