|last time i saw this kind of situation was in school in 1999, Win 95,2000|
how old ur motherboard?
1.So try to make shortcut and turn off through it:
%WinRoot%\system32\shutdown.exe -s -t 00
2.Look in the devices list: if there is Microsoft ACPI, if no then either ur mb too old or installition of XP was not completely succesfull. Also try to change power settings in Bios.
I don know why, but ur XP thinks that u use AT (old, needs to be turned off by button)
instead of ATX power supply.
3. Control Panel -> Power Mangment -> Advanced -> When Shutdown Chosen... or something like that, i don remember exactly cz currently using russian version. So look for that flag and change it.