You can use this PowerShell and WMI combo one-liner to force a shutdown or restart of a remote computer.
(Get-WmiObject -Class Win32_OperatingSystem -ComputerName $Computer).Win32Shutdowntracker(0, "This is a custom comment", 0x00000000, 6)
If you need to provide credentials, you can do something like this:
(Get-WmiObject -Class Win32_OperatingSystem -ComputerName $Computer -Credential $CustomCredentials).Win32Shutdowntracker(0, "This is a custom comment", 0x00000000, 6)