If you are using Windows XP, you can use shutdown.exe. It's in the system32 folder.
Code:
Go to Scheduled Tasks in the Control Panel
> right click > New > Scheduled Task
> rename the task to auto shutdown (or whatever name you want)
> right click the task > Properties
> Task tab
> check Run only if logged on
> Apply
> in the Run field enter:
C:\Windows\system32\shutdown.exe -s -t xx -c "your comment" -f
> Apply
> Schedule tab > set the time and day when you want the task to be run
> OK
where:
s = shutdown
t = time, xx = number of seconds before shutdown
c = comment (
" " are necessary to display your comment)
f = force programs to shutdown
Depending on which drive\folder you have installed XP, you will have to accordingly change the path ( C:\Windows )