Not too sure which command you used to shutdown the machine but try the following :
Open Scheduled Tasks and browse to your C:\WINDOWS\SYSTEM32 folder and find the executible file "Shutdown"
When you finish go to the Advanced settings:
The "Run" line should look like this "C:\WINDOWS\system32\shutdown.exe" now add the following to the end so it will look like this
"C:\WINDOWS\system32\shutdown.exe -r -t 01"
-r will make your system restart, you could use -s to shutdown the system.
Have you got the latest service pack updates on your machine?
Check out this Microsoft site, might help explain why it doesn't work
http://support.microsoft.com/default...b;en-us;814761