DC, Server 2003, Exchange 2003, BackupExec, Sophos, Nothing newly installed... maybe MS updates a couple weeks ago. Certain NO Malware NO virues. These shutdowns started Thu 3/08 out of the blue and continues. The last one was today around 2:03 PM. Dell has a GUI Online Diagnostics that DOES NOT check power supply. Pretty much the results are OK. No event logs except "unexpected shutdown" and the routine startups that follow 15 minutes later.