The following works on most Windows Server 2000 and Windows XP machines, but give it a try:
C:\WINDOWS\SYSTEM32\TSSHUTDN.EXE 0 /DELAY:0 /POWERDOWN
Using the TSShutDn Utility
If you don’t want to use a third-party utility, you may be able to get by with a lesser known utility in Windows 2000 and Windows XP. The native commandline tool tsshutdn.exe was originally designed for shutting down servers, not work stations. It was introduced in Windows 2000, and retained in Windows XP. See MSKB 320188, “How to Use the TSSHUTDN Command to Shut Down a Terminal Server in Windows 2000 Terminal Services,” and MSKB 243202, “Windows 2000 Terminal Services Session Management Tools.” From a command prompt, type tsshutdn /? for a list of its subcommands and syntax. A command line of C:\WINDOWS\SYSTEM32\TSSHUTDN.EXE 0 /DELAY:0 /POWERDOWN will powerdown most Windows 2000 and Windows XP computers, though some (according to correspondent “perris,” who first turned me onto this native utility) will get an error message 1702.