Automatically Turn On a Client Machine

I hope this isn’t too basic for this forum so here it goes…

I was wondering if there was a way to automatically schedule a client workstation to turn on after it has been shutdown. I have a lab of 36 client workstations running Windows XP. It would be great to have them all turn on in the morning. I have been experimenting with the task scheduler using %windir%\system32\shutdown.exe -r -t 0 but when the computer has already been shut down it the task does not execute. Any help would be greatly appreciated.